Systems and methods for indoor positioning using wireless positioning nodes

ABSTRACT

This disclosure provides systems and methods for determining a location of a mobile device within an indoor environment. An embodiment of the system can have one or more positioning nodes (PONs), each having one or more antennas. Each PON can be disposed at a location within indoor environment and configured to transmit signals via the one or more antennas. The signals transmitted from the antennas of the PONs can be synchronized in time and frequency. A server communicatively coupled to the PONs and storing aiding information, including location and signal information related to the PONs, can transmit the aiding information to a mobile device. The mobile device can receive the signals from use the PONs and use the aiding information to determine a three dimensional position within the indoor environment based on one-way time difference of arrival of the signals.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Nonprovisional applicationSer. No. 15/924,093, now patent Ser. No. 10/015,769, entitled “SYSTEMSAND METHODS FOR INDOOR POSITIONING USING WIRELESS POSITIONING NODES,”which claims priority to U.S. Provisional Application, 62/472,412, filedMar. 16, 2017, entitled “INDOOR POSITION LOCATION USING UNSYNCHRONIZEDBEACONS,” U.S. Provisional Application, 62/532,279, filed Jul. 13, 2017,entitled “INDOOR POSITIONING USING WIRELESS SYNCHRONIZED POSITIONINGNODES WITHIN LIGHT BULBS,” and U.S. Provisional Application, 62/561,097,filed Sep. 20, 2017, entitled “INDOOR POSITIONING USING WIRELESSSYNCHRONIZED POSITIONING NODES WITHIN SMOKE DETECTORS, ALARM SENSORS,LIGHT TUBES AND BALLASTS,” the contents of which are hereby incorporatedby reference in their entirety.

BACKGROUND

Technological Field

This disclosure relates to systems and methods for indoor positioningfor wireless mobile devices. More particularly, the disclosure relatesto using one or more positioning nodes (PONs) to establish a threedimensional position for the wireless mobile device.

Related Art

Indoor position location has become increasingly important in today'smobile wireless environment. Applications for indoor position locationcan include retail, advertising, commercial, and residentialenvironments. Currently, among the many available possible indoorposition solutions, a solution based on using low power beacons thatemploys Bluetooth standard has emerged as a popular solution to provideindoor proximity estimates to mobile devices. A mobile device detectingthe transmission of a specific beacon can determine that it is withinclose proximity of that beacon's position relying on estimates oftransmitted and received signal strength. However, such beacontechnology only provides proximity information rather than to determinea three dimensional (e.g., x, y, z) location within an indoor space.

Some beacon-based (e.g., Bluetooth) solutions may rely on estimates ofReceived Signal Strength Indicators (RSSI) to estimate distance betweenthe mobile device and the beacon. The transmitted signal out of thebeacon is of known power and the received signal strength at the mobilereceiver is measured. Employing a model of path loss, the systemattempts to estimate the distance between the mobile device and thebeacon. However, RSSI of RF signals can significantly vary depending onchanging environment and especially as the distance between the mobiledevice and the beacon becomes large. Increased accuracy can requirenumerous low-power beacons, complicating installation for a givenroom/space. On the other hand, to increase range, beacon output power isincreased leading to lower accuracy and shorter battery life. Inaddition, increased power levels can also lead to room or floorambiguity, adversely affecting the utility of the installed beacon(s).Furthermore, even if distance is accurately determined, a single beaconprovides no directional information for the detecting mobile, andtherefore no physical location.

For some applications, knowing precise position rather than justproximity is crucial. For example, applications where robots or dronesare roaming inside a building. If a beacon according to this disclosureis placed in the indoor space and if each robot or drone contains thecircuitry to determine its accurate position according to thisdisclosure, this will lead to much better navigation indoors.

SUMMARY

In general, this disclosure describes systems and methods related tousing one or more PONs to provide a three dimensional position for oneor more mobile devices within an indoor environment. The PONs can haveone or more antennas or emitters. In one embodiment a PON can havemultiple, collocated antennas. In other embodiments, the PONs can eachhave a single antenna. Signals emitted from a single PON having four ormore antennas can provide three dimensional positioning for the one ormore mobile devices. Multiple PONs having fewer than four antennas canalso be used to provide the same three dimensional positioning for theone or more mobile devices. For example, the PONs can be implemented aslight bulbs, smoke detectors, alarm modules, motion detectors, lighttubes, tube ballasts, and various in-home or smart home electronicdevices. The PONs can be ubiquitously deployed within most indoorspaces. The PONs may be connected to main power lines or supply powervia wiring to control unit or battery.

The system disclosed herein can include certain wireless circuitrywithin the PONs configured to emit and/or receive a radiofrequency (RF)ranging signal. The PONs could be standalone or collocated within otherstationary devices (e.g., smart light bulbs, smoke detectors, and alarmmodules). A mobile device (e.g., a smartphone, wireless-enabled tablet,or similar) within the vicinity of one or more PONs can receive theemitted ranging signals. The mobile device can communicate with aninternet accessible server that provides relevant aiding informationallowing the mobile device to determine its indoor location with highaccuracy based on this aiding information along with the timing of theranging signals receives. Such server-provided aiding information caninclude, but is not limited to, the physical location of each PON in thevicinity to aid in position calculation, as well as their code offsetand frequency to aid in detecting their emitted signal and identifyingthe sending PON for each signal.

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One aspect of the disclosure provides a system for determining alocation of a mobile device within an indoor environment. The system canhave a first positioning node (PON). The first PON can have one or moreantennas and disposed in a first location in the indoor environment andconfigured to transmit a first modulated signal via a first antenna. Thesystem can have a second PON having one or more antennas disposed in asecond location in the indoor environment different from the firstlocation and configured to transmit a second modulated signal via asecond antenna. The second modulated signal can be synchronized in timeand frequency with the first modulated signal at a time of transmission.The system can have a server. The server can receive a request from themobile device, the request indicating a coarse location of the mobiledevice, the coarse location being related to a location of the indoorenvironment. The server can transmit aiding information related to firstPON and the second PON based on the request to the mobile device, theaiding information including location information for the first PON andthe second PON, and signal information related to the first modulatedsignal and the second modulated signal. The server can receive aposition report from the mobile device, the position report being basedon a difference in phase between the first modulated signal and thesecond modulated signal at a time of arrival at the mobile device.

Another aspect of the disclosure provides a method for determining alocation of a mobile device within an indoor environment. The method caninclude transmitting, by a first positioning node (PON), a firstmodulated signal via a first antenna, the first PON having one or moreantennas and disposed in a first location in the indoor environment. Themethod can include transmitting, by a second PON, a second modulatedsignal via a second antenna, the second PON having one or more antennasand disposed in a second location in the indoor environment differentfrom the first location, the second modulated signal being synchronizedin time and frequency with the first modulated signal at a time oftransmission. The method can include receiving, at a server, a requestfrom the mobile device indicating a coarse location of the mobiledevice, the coarse location being related to a location of the indoorenvironment. The method can include transmitting, by the server, aidinginformation related to first PON and the second PON, based on therequest to the mobile device, the aiding information including locationinformation for the first PON and the second PON, and signal informationrelated to the first modulated signal and the second modulated signal.The method can include receiving, at the server, a position report fromthe mobile device, the position report being based on a difference inphase between the first modulated signal and the second modulated signalat a time of arrival at the mobile device.

Another aspect of the disclosure provides a method for operating amobile device to determine the location of the mobile device within anindoor environment. The indoor environment can have one or morepositioning nodes (PONs), each PON having one or more antennas. Themethod can include determining, at a mobile device, a coarse location ofthe indoor environment. The method can include transmitting a request toa server including the coarse location, the server storing aidinginformation related to the one or more PONs. The method can includereceiving, at the mobile device, the aiding information from the serverbased on the coarse location. The method can include receiving a firstpositioning signal from a first antenna of the one or more antennas. Themethod can include receiving a second positioning signal from a secondantenna of the one or more antennas, the second positioning being out ofphase with the first positioning signal. The method can includereceiving a third positioning signal from a third antenna of the one ormore antennas, the third positioning signal being out of phase with thefirst positioning signal and the second positioning signal. The methodcan include determining a position mobile device based on a one-waytime-difference of arrival (TDOA) between the first positioning signal,the second positioning signal, and the third positioning signal.

Other features and advantages of the present disclosure should beapparent from the following description which illustrates, by way ofexample, aspects of the disclosure.

BRIEF DESCRIPTION OF THE FIGURES

The details of embodiments of the present disclosure, both as to theirstructure and operation, may be gleaned in part by study of theaccompanying drawings, in which like reference numerals refer to likeparts, and in which:

FIG. 1 is a graphical depiction of an embodiment of an indoorpositioning system for a mobile device;

FIG. 2 is a functional block diagram of an embodiment of the positioningnode of FIG. 1;

FIG. 3 is a graphical depiction of an embodiment of an arrangement ofthe antennas of the PON of FIG. 2;

FIG. 4 is a graphical depiction of a method for determiningtwo-dimensional location for the mobile device of FIG. 1;

FIG. 5 is a graphical depiction of a method for determiningthree-dimensional location for the mobile device of FIG. 1;

FIG. 6 is a functional block diagram of an embodiment of aradiofrequency front end of the positioning node of FIG. 2;

FIG. 7 is a functional block diagram of an embodiment of a delay networkfor use with the RF front end 600 of FIG. 6;

FIG. 8 is a functional block diagram of another embodiment of the delaynetwork for use with the RF front end of FIG. 6;

FIG. 9 is a functional block diagram of an embodiment of aradiofrequency front end for the positioning node of FIG. 1; and

FIG. 10 is a functional block diagram of an embodiment of a portion ofthe positioning node of FIG. 1.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theaccompanying drawings, is intended as a description of variousembodiments and is not intended to represent the only embodiments inwhich the disclosure may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof the embodiments. However, it will be apparent to those skilled in theart that the disclosure without these specific details. In someinstances, well-known structures and components are shown in simplifiedform for brevity of description.

FIG. 1 is a graphical depiction of an embodiment of an indoorpositioning system for a mobile device. An indoor positioning system(system) 100 can have a mobile device 102. The mobile device 102 can bea smart phone or other mobile electronic device including softwareand/or hardware as disclosed herein. The mobile device 102 can becommunicatively coupled to a server 120 via a wide area network (WAN) ornetwork 104. The network 104 can be, for example, the Internet or otherapplicable wireless network. The system 100 can be associated with ormove in and out of an indoor environment 106. The system 100 can haveone or more positioning nodes (PONs) 110 located within the indoorenvironment 106 with the mobile device 102. The PONs 110 may also bereferred to herein simply as beacons or nodes. The PONs 110 are labeledas PON 110 a, PON 110 b, PON 110 c, and PON 110 d, but may referred tocollectively as PONs 110. Each PON 110 can transmit one or more signals112 (shown as a signal 112 a, a signal 112 b, a signal 112 c, a signal112D) that the mobile device 102 can use to determine athree-dimensional position within the indoor environment 106. Thesignals 112 are continuously or periodically transmitted, as required.For ease of description, the PONs 110 are depicted as each transmittinga single signal 112. However as described in the following, each of thePONs 110 may have one or more antennas, where each antenna can transmita respective version of the signal 112. Thus each PON 110 can actuallytransmit one or more signals 112 as needed according to the followingembodiments.

As the mobile device 102 moves indoors, it may not have sufficientsignal to provide precise positioning via, for example, a globalpositioning system (GPS) signal. The mobile device 102 may initiallydetermine an approximate or general physical position of the indoorenvironment 106 based on a coarse location via a last known outdoorlocation, via GPS location of the mobile device 102, for example. Insome other examples, the mobile device 102 can determine a coarselocation based on Wi-Fi signals from one or more networks in the localarea or even within the indoor environment 106. In addition, while aWi-Fi signal may provide general location, that is, somewhere inside agiven building, such location information is still “coarse” in terms ofthe indoor positioning system disclosed herein. In some embodiments, thesignals 112 transmitted by the PONs 110 can also include an indicationof approximate position of the indoor environment 106. In someembodiments, the coarse position may be of the size of the localvicinity spanning one or more rooms within an identified building and isused by the server 120 to provide the appropriate aiding information.

The mobile device 102 can determine its coarse location, for example, inwhich building or which part of a building, within several rooms. Themobile device 102 can accomplish this determination using last knownGPS, Wi-Fi or having received the signal 112 from at least one PON 110.This coarse location information can then be sent to the server 120. Theserver 120 can then provide the aiding information including thelocation of each close PON 110 and their identifying signalcharacteristics so the mobile device 102 can detect them and canattribute each received signal 112 to the corresponding PON 110. Themobile device 102 can use this information to look for all the PONs 110within the indoor environment 106. Using the location of each PON 110,the mobile device 102 can determine its three dimensional location,using four signals 112, for example. In some embodiments, the mobiledevice 102 can use three signals 112 to determine a two dimensionalposition within the indoor environment 106. Similarly, with only twosignals 112, the mobile device 102 can determine a one dimensionalposition. The mobile device 102 can then optionally report the computedposition back to the server 120.

Having determined an approximate or coarse location, the mobile device102 can communicate with a server 120 via the network 104. The server120 can then transmit information related to the location of each of thePONs 110. Such information can include the locations and signalcharacteristics of all the PONs 110 within the indoor environment 106.Using this information, the mobile device 102 can then detect andprocess the signals (e.g., the signals 112) received from the PONs 110to determine its three-dimensional position within the indoorenvironment 106. The mobile device 102 can then optionally report thecomputer location to the server 120 to aid in continued calibration andaccuracy improvement of the PONs 110.

As described in the following, certain embodiments of the PON 110 can bea single, stand-alone device having one or multiple antennas. In someembodiments, the PONs 110 can be co-located with various smart devices,Internet of things (IOT) devices, and other common household systems.The PONs 110 may continuously or periodically transmit and receivemulti-tiered ranging signals from within smoke detectors, alarm modules,light bulbs, ballasts and other IoT or smart appliances or fixtures. Insome ranging systems, higher positioning resolution may require morecomplex and higher power consuming utilized circuitry. In someembodiments, the system 100, the PONs 110 more specifically, cantransmit a multi-tiered ranging signal that can accommodate applicationswith various desired levels of accuracy. In applications not requiringthe highest possible accuracy are able to determine their location attheir lower required accuracy using less complex circuits and lesspower. Smoke detectors, alarm sensors, light bulbs/tubes, ballasts, IoTdevices, smart appliances, and the like may be referred to herein ascontaining devices (CDs). CDs are generally any device that can containthe PONs 110. In some embodiments CDs like a smoke detector or lightbulbmay have confined or limited space constraints. Accordingly, suchdevices may only accommodate a single or at least a limited number ofantennas. In some other embodiments the PONs 110 can also be standalonepositioning devices (e.g., not within a CD) having more than one antennaand in some cases four or more antennas.

An advantage of co-locating PONs 110 within smoke detectors, alarmsensors, light tubes, or other common household devices is their commonpresence in most indoor locations and generally simple, one-for-onereplacement. In addition, they may already have a constant continuouspower source that can be used for co-located PONs 110.

In some embodiments, the PONs 110 co-located with an existing householddevice or CD can also take advantage of preexisting wiring orelectrical/electronic backbone within the indoor environment 106. Suchpre-existing wiring can provide a constant continuous source of power inaddition to a time or frequency reference. The common time or frequencyreference can be important for synchronizing the timing and frequenciesof the PONs 110 within the same vicinity, as described in more detailbelow.

These CDs may already perform various electronic operations.Accordingly, the additional silicon area required added positioningbeacon/PON capability may not dramatically increase the cost ofmanufacturing. In addition, the PON 110 can leverage much of the commoncircuit circuitry already existing within the CD.

In some other embodiments, the PONs 110 can be hardwired to a continuouspower source within the indoor environment 106 or can have anindependent power supply such as a battery. Such PONs 110 can be astandalone device. As described below, some embodiments of the PONs 110can have four or more antennas. A single PON 110 having four or moreantennas can independently provide a 3D position to the mobile device102.

In some embodiments, the system 100 can allow unlimited simultaneoususers. That is, any number of mobile devices 102 can be present withinthe indoor environment 106 and use the PONs 110 to determinethree-dimensional positions within the indoor environment 106.

The mobile device 102 can use a known position of the PONs 110 (e.g.,from the server 120) in addition to time and distance traveled by thesignals 112 to determine its own position. In a one-way time of arrival(OW-TOA) positioning scheme, the clocks of all PONs 110 (in the indoorenvironment 106) and the mobile device 102 must be preciselysynchronized. While Synchronization among the PONs 110 within the indoorenvironment 106 is feasible, as described below, requiringsynchronization between the PONs and any and all mobile devices enteringthe environment may not be feasible. Therefore, a variant of the OW-TOAis one-way time difference of arrival (OW-TDOA), in which the clocks ofthe PONs 110 are synchronized among each other but clock synchronizationwith the mobile device 102 is not required. In OW-TDOA, the clock of themobile device 102 may not be synchronized with the PONs 110. The clockof the mobile device 102 can have an offset relative to the synchronizedclocks of the PONs 110. OW-TDOA handles this unknown or random timeoffset of the mobile device 102 by requiring one more antennameasurements over what OW-TOA would require but eliminates the need forthe mobile devices to be synchronized with the PONs 110 in the indoorenvironment 106.

In some examples, an OW-TDOA methodology can eliminate certain multiuserrestrictions caused by long processing or communication delays if aTwo-Way ranging system was used. In OW-TDOA, ranging nodes (e.g., thePONs 110) can continuously transmit the signals 112 that the mobiledevices 102 can use to determine a three-dimensional position. In someembodiments the mobile device 102 may not transmit ranging signals backto, or directly synchronize with the PONs 110. Accordingly, all of thePONs 110 can have a common or synchronized clock. This synchronizationis relatively simple in a single PON 110 having multiple (e.g., four ormore antennas). Four signals 112 being transmitted from antennas in asingle PON 110 can readily have a common timing source (e.g., aninternal local oscillator). In the PONs 110 having only one, two, orthree antennas, or the PONs 110 distributed among different devices(e.g., CDs), other synchronization methods may be required. For example,the PONs 110 implemented in four distinct and separate light bulbsdistributed within the indoor environment 106 may all receive power froma common source such as a main power network within a building. Thus, inat least one example, the PONs 110 can use the frequency of such powersource as their synchronization signal.

FIG. 2 is a functional block diagram of an embodiment of the positioningnode of FIG. 1. In some embodiments, a PON 200 can be similar to thePONs 110. The PON 200 can have a controller 202. The controller 202 cancontrol the overall functions of the PON 200. For example, thecontroller 202 can control the transmission of the signals 112 from theantennas 210. The controller 202 can have a central processing unit(CPU) 204. The CPU 204 also be implemented as one or more processors ormicroprocessors. The CPU 204 can have at least one reference oscillatoror clock to maintain timing synchronization for the PON 200. Thereference oscillator can have, for example a local oscillator (LO) usedto synchronize the PON 200 with one or more other PONs (e.g., PON 110).

The controller 202 can also include a modem (not shown) or becommunicatively coupled to a modem of the CD, for example. For ease ofdescription, the performance of certain functions may be describedherein in terms of the PON 200 however, the CPU 204 or the controller202 may actually perform such functions.

The PON 200 can have a memory 206. The memory 206 can store informationrelated to other PONs 110, 200 in addition to instructions or code forthe performance of various tasks associated with indoor positioning forthe mobile device 102. The memory 206 can receive and store data andother information related to the signals 112 and their respectivesynchronization with the signals 112 from the other PONs 110.

The PON 200 can also have a power supply 208. The power supply 208 canhave one or more power storage components, such as battery. Such batterycan be rechargeable or user replaceable. In some embodiments, the powersupply 208 can be a hardware power supply such as main power supply in abuilding. In such a case, the power supply 208 can be for example, 110V, 120V, and 50 or 60 cycle power, for example. Other configurations arealso possible as described below.

The PON 200 can have one or more antennas 210. The PON 200 is shown withthree antennas 210 a, 210 b, 210 n, but can have a single antenna 210.The PON 200 can also have two, three, four or more antennas 210 asindicated by the ellipsis in FIG. 2.

The PON 200 can have at least one transmitter 211. The transmitter 211can be coupled to one or more antennas 210 to transmit the signal 112for example. The PON 200 can also have a receiver 212 configured toreceive signals or various types of communication via the antennas 210(e.g., the antenna 210 a for example). In some embodiments, each of theantennas 210 can have a corresponding transmitter 211 (e.g., multipletransmitters 211 per PON 200). In embodiments in which the PON 200 hasmultiple antennas 210, each of the antennas 210 may be driven by its owntransmitter 211. In such embodiments, only one of the antennas 210 maybe coupled to the receiver 212. In some embodiments the PON 200 may nothave the receiver 212 as the PON 200 may be implemented only fortransmitting the signals 112.

In some embodiments the transmitter 211 in the receiver 212 can becombined in a transceiver 214. The transceiver 214 can combine thefunctions of the transmitter 211 and receiver 212 in order to coupleupon to one or more communication networks via the antennas 210. Thetransceiver 214 can also implement various RF front end components andcapabilities. The RF front end can include for example, one or morefilters, amplifiers e.g., power amplifier or low noise amplifier),mixers, and LOs. The transceiver 214 can further couple the PON 200 tothe (wireless) network 120 via the antenna(s) 210.

The PON 200 can also have a communications bus 216. The communicationsbus 216 can communicatively couple the above described components of thePON 200.

In one embodiment, the PON 200 can simply have the transmitter 211 and asingle antenna 210, as opposed to the transceiver 214 and multipleantennas 210. In the single antenna configuration, the PON 200 can beused in coordination with other PONs 200 (e.g., multiple PONs 110) toprovide indoor location capability for the mobile device 102. Asdescribed in more detail below, four or more signals 112 may be requiredto provide three dimensional positioning for the mobile device 102.Accordingly, four single antenna PONs 200 may be required to providesuch location determination for the mobile device 102.

In a multi-antenna configuration, each PON 200 can each have four ormore antennas. The antennas 210 can be geometrically arranged and eachtransmit distinguishable signals 112 that are received at the mobiledevice 102 (FIG. 3). The signals transmitted from the antennas 210 showncan be different but internally synchronized signals. That is, thesignals a synchronized in time, phase, and frequency. In some examples,the antennas 210 may not be physically arranged in a linear manner (FIG.3).

In some embodiments, the PON 200 can also have two or three antennas210. In such an embodiment, multiple PONs 200 may be required in orderto provide the four signals 112 to the mobile device 102.

The PON 200 can implement one of multiple radio access technologies. Forexample, direct sequence spread spectrum (DSSS) can be used for thesignals 112. By examining the received carrier phase relationships amongthe distinguishable received signals (e.g., signals 112) the mobiledevice 102 can determine its three-dimensional location relative to thedetected (multi-antenna) PON 200. In DSSS, each of the signals 112 isdistinguished from other signals using different code offsets. The PON200, or group of PONs 200, emitting more than three signals 112 oradditional beacons within the indoor environment 106 can provideredundancy to the solution and increase accuracy. In some example, themore signals 112 that the mobile device 102 receives, the more accuratethe three dimensional position determination becomes.

FIG. 3 is a graphical depiction of an embodiment of an arrangement ofthe antennas of the positioning node of FIG. 2. In an embodiment, thePON 200 can have a cluster 300 of four antennas 210 a, 210 b, 210 c, 210d, placing the (main) antenna 210 a at the center of the cluster. Insome embodiments, the other three (additional) antennas 210 b, 210 c,210 d, can be placed along the circumference of the circle (shown indashed lines) centered on the antenna 210. For ease of description, onlya single transceiver 214 is shown in FIG. 3. However, similar to above,each of the antennas 210 of the cluster 300 may be coupled to anindividual or its own transmitter 211 (e.g., transceiver 214).

Locations of the additional antennas 210 may be chosen such that nothree antennas, including the antenna 210 a, lie the same line. That is,they may not be arranged in a linear manner. The antenna 210 a has beenlabeled with M (e.g., for ‘main’), the antenna 211 is labeled with an N,the antenna 212 is labeled with SW, and antenna 213 is labeled with SW.The N, SW, SE are exemplary directional labels, correspondingrespectively to North, Southwest, and Southeast. A linear arrangement oftwo or more of the antennas 210 a, 210 b, 210 c, 210 d is possible(e.g., FIG. 4), however the precision of the indoor position provided tothe mobile device 102 may be reduced.

In an embodiment, the PON 200 can emit a DSSS Bi-Phase Shift Keyed(BPSK) modulated RF signal (e.g., the signal 112) via the antenna 210 a.This may be referred to as the main signal. The PON 200 can also emit,or transmit, delayed copies of this DSSS main signal from the otherantennas N, SW and SE. For example, the signals radiating from N, SW,and SE can be copies of the (main) signal 112 from the antenna 210 a (M)delayed by time delays d-N, d-SW and d_SE, respectively where “d”indicates a period of the delay. A DSSS signal delayed by more than onespreading chip is distinguishable at the receiver (e.g., the mobiledevice 102) from the main signal. Hence if d_N, d_SW and d_SE are allgreater than one spreading chip period from the main signal 112 from theantenna 210 a, and are more than one spreading chip period apart fromeach other, the mobile device 102 can distinguish among the variousreceived signals 112 from the PON 200. As used herein, a chip is a pulseof a direct-sequence spread spectrum (DSSS) code, such as a PseudorandomNoise (PN) code sequence used in direct-sequence code division multipleaccess (CDMA) channel access technique.

Assuming the delays d_N, d_SW and d_SE are known and their respectiveantennas are stationary, mobile device 102 can adjust for timedifference as if they were all transmitted from their respectiveantennas 210 b, 210 c, 210 d at the same instant. After such adjustmentby the mobile device 102, the computed time difference of arrival of thevarious copies of the signal 112 is a function of the difference in freeair path delay among the four signals 212. If all of the signals 112 aretransmitted from the antennas 210 a, 210 b, 210 c, 210 d at the sametime, after correcting for the known inserted delays “d”, then eachsignal 112 can arrive at mobile device 102 after their free air pathdelay. Since the mobile device 102 and the PON 200 are not synchronizedto a global time reference, the free air path is not measurable byexamining any (single) one of the distinguishable signals 112. However,the mobile device 102 can determine both the angles between the signals112 and the mobile device 102, as well as the range based on thedifference in arrivals of the distinguishable signals 112 from that PON200.

As noted above, the PON 200 can have can have fewer than four antennas210. In order to provide sufficient information to the mobile device 102for three dimensional position determination, the number of signals 112received at the mobile device 102 may be greater than or equal to four.Thus, in some embodiments, multiple PONs 200 (having fewer than fourantennas 210) may be required for three dimensional positiondetermination within the indoor environment 106. This may require, forexample, two PONs 200 having two antennas 210 each, four single antennaPONs 200, or other combinations amounting to four or more antennas 210,each transmitting a signal. In the presence of fewer than four signals112 from an associated fewer than four antennas 210, the mobile device102 can determine a two dimensional position using three signals 112 ora one dimensional position using two signals 112.

FIG. 4 is a graphical depiction of a method for determiningtwo-dimensional location for the mobile device of FIG. 1. In the exampleof FIG. 4, the signals 112 can be received at the mobile device 102 fromthree antennas 410, 411, 412. The three antennas 410, 411, 412 can beimplemented within the same PON 200 or they may be antennas fromseparate or distributed (or single-antenna) PONs 200 having a signalantenna. For example, three single-antenna PONs 200 can be disposed in alinear arrangement within a containing device, such as a lightingfixture (e.g., a fluorescent light tube), in a linear arrangement. Theantennas 410, 411, 412 can also be disposed within a single PON 200.

The antenna (main antenna) 410, denoted by m, and a left antenna 411,denoted by subscript a, and a right antenna 412, denoted by subscript b.In this example, all antennas 410, 411, 412 are co-linear forillustration purposes but they do not need to be in an actualimplementation. Indeed, it may be advantageous in certain situations ifthe antennas are not co-linear. The mobile device 102, is denoted by T(T is for target).

The distances of antennas 411, 412 from the main antenna 410 are d_(a)and d_(b) respectively. X_(m) denotes the distance between the mainantenna 410, M, and the mobile device 102, T. Distances X_(a) and X_(b)denote the distance from the target mobile, T, to antennas 411, 412respectively. The angle Ø_(a) is the angle T→m→a, while the angle Ø_(b)is the angle T→m→b. Choosing a, m and b to be co-linear results inØ_(b)=180−Ø_(a) and simplifies the math of this 2D example. Fromtrigonometry, we know that,X _(a) ² =d _(a) ² +X _(m) ²−2d _(a) X _(m) cos Ø_(a)  (1)And,X _(b) ² =d _(b) ² +X _(m) ²−2d _(b) X _(m) cos Ø_(b)  (2)

Let X_(a)−X_(m)=P_(a)+n_(a)λ were λ is the carrier wavelength, n_(a) isan integer and P_(a) is the fractional wavelength part of thedifference. Because both d_(a) and d_(b) are in this example assumed tobe less than λ, regardless of where T might be in the plane, X_(a)−X_(m)and X_(b)−X_(m) will always be less than λ and n_(a)=0. We can thereforewrite X_(a)−X_(m)=P_(a) and X_(b)−X_(m)=P_(b). Plugging into (1) and (2)and simplifying,P _(a) ² −d _(a) ²=−2X _(m)(P _(a)−2d _(a) cos Ø_(a))  (3)P _(b) ² −d _(b) ²=−2X _(m)(P _(b)−2d _(b) cos Ø_(b))  (4)Given that Ø_(b)=180−Ø_(a), hence cos Ø_(a)=−cos Ø_(b). Solving forX_(m),

$\begin{matrix}{X_{m} = \frac{\left( {P_{a}^{2} - d_{a}^{2}} \right) + \left( {P_{b}^{2} - d_{b}^{2}} \right)}{{- 2}\left( {P_{a} + P_{b}} \right)}} & (5)\end{matrix}$then use X_(m) and (1) or (2) to solve for Ø_(a).

The range X_(m) from the main radiator to T and the angle Ø_(a) can besolved knowing the carrier phase differences P_(a) and P_(b). Thelocation of the point T can then be computed bas on the known positionsof m (as it is determined during installation) and the orientation ofthe line a→m→b in the 2D plane. We now relax the assumption that bothd_(a) and d_(b) are less than λ hence n_(a). may not be assumed toalways equal zero. This means that measured P_(a) would be ambiguous byan integer number of carrier cycles. This is known in the field ofoutdoor positioning as the carrier integer ambiguity and numeroustechniques that are well known in the art are available to mitigate itseffects.

FIG. 5 is a graphical depiction of a method for determiningthree-dimensional location for the mobile device of FIG. 1. Thearrangement of FIG. 4 can be generalized to the 3D case as shown in FIG.5. The 3D case shown corresponds to the arrangement of four singleantenna PONs (e.g., the PON 200 having one antenna 210). For the 3Dgeneral case four other, delayed antennas around the main antenna m 530.The minimum required set for the 3D case is three antennas, or emitters,in addition to the center main antenna m. The additional three antennasare labeled antenna a, 532, antenna b 533, and antenna c 534. Thedistance between the antennas a, b, c and the main antenna 530 m are,respectively, distances d_(a), d_(b) and d_(c) as shown. The location ofeach antenna may be identified by the unit vector anchored at the mainantenna 530 and by the distance of the respective antenna 532, 533, 534from m. For example, the antenna a 532 is located along the unit vector

=a_(x)î+a_(y)ĵ+a_(z){circumflex over (k)} and is d_(a) away from m. Theexample above, a_(z), b_(z) and c_(z) are zero for the two-dimensionalcase where all the antennas lie in a plane. However the antennas neednot be co-planar. In some examples, it may be more advantageous if theantennas are not arranged in a co-planar manner because to eliminate asymmetric solution located behind the planar beacon. The radiatingantennas may be of the type that has a conducting reflecting plane andhence radiate only towards the front of the beacon (e.g., the PON 110)with minimal radiation toward the back of the beacon.

As in the 2D case, the distance from antennas 530, 532, 533, 534 to themobile device 102 at T are X_(a), X_(b), X_(c) and X_(m). The term{circumflex over (V)} is defined as the unit vector anchored at m andpointing to the target T (e.g., the mobile device 102).{circumflex over (V)}=V _(x) î+V _(y) +ĵ+V _(z) {circumflex over (k)}

Calculating {circumflex over (V)} and X_(m), provides the 3D coordinatesof the mobile device 102 at point T (target). From FIG. 5, Ø_(b) is theangle that the range line Xm forms with the vector

that defines the location of the antenna b 533. Similarly, for antenna a532 and antenna c 534. Trigonometry provides,({circumflex over (V)}·

)/|

|=cos Ø_(a)and|

|=1thenV _(x) a _(x) +V _(y) a _(y)=cos Ø_(a)  (6)V _(x) b _(x) +V _(y) b _(y)=cos Ø_(b)  (7)V _(x) c _(x) +V _(y) c _(y)=cos Ø_(c)  (8)

The terms a_(z), b_(z), and c_(z) are zero in this example.Additionally, Ø_(a), Ø_(b) and Ø_(c) are not independent variables sinceany two angles fully define the third. In fact,

$\begin{matrix}{{{\cos\;\varnothing_{c}} = {{{CC}_{a}\cos\;\varnothing_{a}} + {{CC}_{b}\cos\;\varnothing_{b}}}}{{where},{{CC}_{a} = {\frac{{c_{x}b_{y}} - {c_{y}b_{x}}}{{a_{x}b_{y}} - {a_{y}b_{x}}}\mspace{14mu}{and}}},{{CC}_{b} = \frac{{c_{y}a_{x}} - {c_{x}a_{y}}}{{a_{x}b_{y}} - {a_{y}b_{x}}}}}} & (9)\end{matrix}$Similar to the 2D example above, in 3DP _(a) ² −d _(a) ²=−2X _(m)(P _(a) −d _(a) cos Ø_(a))  (10)P _(b) ² −d _(b) ²=−2X _(m)(P _(b) −d _(b) cos Ø_(b))  (11)P _(c) ² −d _(c) ²=−2X _(m)(P _(c) −d _(c) cos Ø_(c))  (12)Solving for X_(m),

$\begin{matrix}{{X_{m} = \frac{\left( {P_{c}^{2} - d_{c}^{2}} \right) - {{CA}\left( {P_{a}^{2} - d_{a}^{2}} \right)} - {{CB}\left( {P_{b}^{2} - d_{b}^{2}} \right)}}{\left( {- 2} \right)\left( {P_{c} - {CAP}_{a} - {CBP}_{b}} \right)}}{where}{{{CA} = \frac{\left( {d_{c}{CC}_{a}} \right)}{d_{a}}},{{{and}\mspace{14mu}{CB}} = \frac{\left( {d_{c}{CC}_{b}} \right)}{d_{b}}}}} & (13)\end{matrix}$Using X_(m) and equations (10), (11), can allow a determination of Ø_(a)and Ø_(b).

From combining equations (6), (7) and (8) we know that,

$\begin{matrix}{V_{x} = \frac{{b_{y}\cos\;\varnothing_{a}} - {a_{y}\cos\;\varnothing_{b}}}{{a_{x}b_{y}} - {a_{y}b_{x}}}} & (14) \\{V_{y} = \frac{{a_{x}\cos\;\varnothing_{b}} - {b_{x}\cos\;\varnothing_{a}}}{{a_{x}b_{y}} - {a_{y}b_{x}}}} & (15)\end{matrix}$and {circumflex over (V)} being a unit vector,V _(z)=√{square root over (1−V _(x) ² −V _(y) ²)}

This provides X_(m), V_(x), V_(y) and V_(z). The location of the targetT is (T_(x), T_(y), T_(z)) is then,T _(x) =X _(m) V _(x) , T _(y) =X _(m) V _(y) and T _(z) =X _(m) V _(z)

In cases where solving the angles without computing X_(m) is desirable,that is, when two antennas are used, we can eliminate X_(m) by combiningthe equations and calculate Ø_(a), Ø_(b) and Ø_(c) directly withoutX_(m). This is useful because X_(m) is sensitive to noise due to therelative proximity of the antennas. However calculation of Ø_(a), Ø_(b)and Ø_(c) are not as sensitive. The above 2D and 3D solution exampleswere provided as one implementation of resolving a 3D position usingfour measurements, in the 3D case. We want to emphasize that these areonly examples of computations that could be performed to yield thelocation. They are by no means the only way to arrive at a location.

In some examples, the PONs 110 (or the PON 200) can be placed in one ormore accessible locations within the indoor environment 106. This can beat one or more points on the ceiling or high on one or more walls toprovide an unobstructed path between the PONs 110 and mobile device 102in the indoor environment 106. The mobile device 102 can receive thesignals 112 and compute the distance and azimuth to the antennas and thePON(s) 110. The mobile device 102 can then compute its 3D orientationbased on the positions of the PONs 110. In some embodiments, thisinformation can further be uploaded to the server 120 to be used byother mobile device 102 entering the indoor environment 106 in thefuture. When mobile device 102 enters the room (e.g., the indoorenvironment 106), it can detect an identifying signal from the PON 110.

In another example, the mobile device 102 can have a camera. The cameracan take several photos of the indoor environment 106 such that theresulting photos overlap in coverage. Each time a photo is snapped, themobile device 102 can perform a location determination based on thesignals 112 from the PON 110 and record the result. The overlappingphotos of the room can be used to construct a 3D model of the indoorenvironment 106. In addition, because the mobile device 102 performs alocation measurement with every photo, the mobile device 102 can alsoaccurately determine the location and orientation of the PON 110 and itsrelationship to the 3D model of the interior of the indoor environment106. This method constructs a 3D model of the room and locates thePON(s) 110. This 3D map is very valuable to applications needing to takeadvantage of this new localization ability. Also, the x, y, z locationof the mobile device 102 may then be available within a useful contextof the 3D model of the room including obstacles, furniture, appliances,points of interest, etc.

FIG. 6 is a functional block diagram of an embodiment of aradiofrequency front end of the positioning node of FIG. 2. The PON 200can have an RF front end 600. The RF front end 600 can be coupled to thecontroller 202 (FIG. 2) for example. The RF front end 600 can have manyof the same features or components and perform the same or similar tasksas the transceiver 214, for example.

In some embodiments, the RF front end 600 can be used to periodicallytransmit the signal 112. As described above, certain embodiments may notrequire a receive chain because the PON 200 may not be required tonecessarily receive external signals. Thus at a minimum the RF front end600 has at least one RF transmit chain 630 driving each antenna 610.Multiple RF transmit chains 630 are shown for ease of description,however the PON 200 may only have one antenna 210 and thus a singletransmit chain 630 driving one antenna 610. As described below however,there may also be certain advantages to having a receive chain.

The controller 202 can be coupled to one or more antennas 610 (shown asantennas 610 a-610 n) via the RF front end 600. The RF front end 600 canhave one or more RF upconversion, or transmit chains 630. The ellipsesin FIG. 6 indicate the use of multiple antennas 610 a-610 n in the RFfront end 600. For ease of description, the elements of the transmitchain 630 a are the primary example of the following description,however the features and characteristics are equally applicable toadditional transmit chains 630 as needed for multi-antennaimplementations.

Lowpass filtered digital data from the baseband and applicationprocessors (e.g., the CPU 204) can be received at an in-phase andquadrature-phase (I & Q) ports 607, 608. A digital to analog converters(DAC) 605 can convert the digital samples stream to continuous-timeanalog signal. The I and Q analog signals can be provided to quadratureupconverter having I and Q mixers 604 and a 90-degree phase shifter 612.Each transmit chain can have a local oscillator (LO) 606 that generatesa continuous sinusoid at the carrier frequency. The LO 606 can becoupled to a time reference 642. The time reference 642 can be used tocontrol the oscillation of all of the LOs 606 of each transmit chain630. Alternatively, there may be one time reference 642 controlling oneLO 606 and the output of such LO 606 can be shared among all of thetransmit chains 630. The time reference can ensure that all transmitchains 630 are synchronized. In some embodiments having only a singletransmit chain 630, the RF front end 600 can implement other types ofsynchronization as described below.

The output of the LO 606 can be split into in-phase (I) and quadrature(Q) phase components and fed into the mixers 304. The output of themixers 604 can be combined using combiner 603, and then passes through apower amplifier (PA) 602. The output of the PA 602 can flow through abandpass filter 609 to reduce out-of-band emissions. An additionalfilter (not shown) performing a similar function to the bandpass filter609 can also be placed between the combiner 603 and the power amplifier602. The transmit RF signal is then available at the (RF) output port601 a for transmission via an antenna 610 a. This process can form themain RF signal transmitted via the RF front end 600.

In embodiments in which the RF front end 600 is coupled to multipleantennas 610, multiple transmit chains 630 may be present and coupled tothe associated antennas 610 n. The additional signal(s) 112 transmittedvia the antennas 610 n can be delayed from the main signal 112transmitted by the antenna 610 a. The delay can be incorporated into thecorresponding signals 112 via analog or digital circuitry. In someembodiments certain hardware can include a time delay 640 for eachdelayed signal copy, each transmitter to its own radiating antenna 610n. The original digital data stream feeding I and Q input ports 607 and608 (e.g., from the CPU 620) can be copied into multiple streams witheach stream delayed from the others by the required amount. This can beaccomplished by inserting a digital shift registers (e.g., the timedelay 640) into the respective digital transmit chains 630 to achievethe required amount of delay for each transmit stream. In someembodiments, such a digital shift, or time delay, can be the minimumdelay required for the receiver to distinguish among the distinctsignals 112. In case of PN sequence BPSK or QPSK (quadrature phase shiftkeying) driven DSSS modulation, each signal 112 can differ in delay fromall other signals 112 by at least one PN sequence clock period. Thisdifference can be a separation of one chip period, for example. Someapplications may require a separation of more than one chip period toprovide guard time.

FIG. 7 is a functional block diagram of an embodiment of a delay networkfor use with the RF front end 600 of FIG. 6. In embodiments implementingan analog delay, the delay can be included after upconversion but priortransmission by the antenna 610 n. Accordingly, the time delay 640 ofFIG. 6 can be omitted in embodiments using the analog delay network 700of FIG. 7. The analog delay could use Surface Acoustic Wave (SAW) delaylines as an example. In some examples, a delay network 700 can be usedto generate the delayed copies at RF as in FIG. 6. In this analogimplementation, the RF signal from port 601 a in FIG. 6 can be providedto a RF power splitter 702 before transmission via the antennas 610. Theoutputs of the RF power splitter 702 can each be directed to its ownrespective SAW delay line (delay line) 704. SAW delay lines are similarin construction to the SAW filters used in RF circuits for filtering.The delay lines 704 are depicted as delay-0 704 a, delay-1 704 b,delay-c 704 c, delay-n 704 n. Each of the delay lines 704 can have adifferent delay time. The output of each of the delay lines 704 can befed to a respective antenna 610. Each delay line can have of a separatedelay element or delay line 704. An embodiment may use the same SAWsubstrate for all the delays. This can ensure that all the delaysrespond proportionally to variations in ambient temperature andmanufacturing and aging effects. In a PON having a single antenna, thedelay network 700 may not be present. An advantage of using analog delaylines is now we only need to use one transmit chain 630 to drive thepower splitter that drives as many distinct antennas 610 may be neededfrom the splitter.

With reference to FIG. 6 and FIG. 7, two primary methods for delayingthe main signal 112 for each additional antenna 610 are disclosed. Insome examples, delayed copies of the signals 112 transmitted from theantennas 610 are advantageous because it allows the mobile device 102 todistinguish the origin of each copy of the main signal 112 (e.g.,transmitted from the antenna 610 a). This can be thought of as amultiple access method to separate the various copies of the main signal112. Using either analog or digital delays that are more than onespreading chip period different from one another allows implementationof Code Division Multiple Access (CDMA) techniques as outlined above.

FIG. 8 is a functional block diagram of another embodiment of the delaynetwork for use with the RF front end of FIG. 6. In some embodiments, aswitching network 800 can be implemented between the port 601 a and theantennas 610. The switching network 800 can use Time Division MultipleAccess (TDMA) techniques to selectively select the transmissions via theRF transmit chain 630. In some embodiments, only one RF transmit chain630 (FIG. 6) may be needed. The RF signal from port 601 a can besupplied to a switching matrix 802. The switching matrix 802 canalternately connect the output port 601 a to a number of bandpassfilters 806. The bandpass filters are shown as 806 a, 806 b, 806 c, 806n, but may referred to collectively as bandpass filters 806.

The switching matrix 802 can have an input port 808. The input port 808can receive a switching control input from, for example, the controller202. This control input can be used to indicate to the switching matrix802 which antenna 610 is selected for transmission. The antenna pathscan be sequentially selected to transmit. The time between transmissionscan be analogous to the delay period described above.

In some examples, the signal 112 transmitted by the various antennas 610can be modulated to identify the antenna 610 from which it wastransmitted. Generally, any multiple access method can be used totransmit the signal from the different antennas 610 while at the sametime allowing the receiver to distinguish which signal 112 or signalcomponent came from which antenna 610.

FIG. 9 is a functional block diagram of an embodiment of aradiofrequency front end for the positioning node of FIG. 1. A front end900 can have a transmit chain 630 and receive chain 640. As noted above,there may be more than one RF transmit chain 630, however, for ease ofdescription, only one RF transmit chain 630 a is shown in FIG. 9. In theRF receive chain 640, a received signal can be received at the antenna610 b and a port 611. The receive chain 640 can also have a bandpassfilter 619 coupled to the port 611. The receive chain 640 can also havea very variable gain amplifier 612 (e.g., low noise amplifier or LNA).The variable gain amplifier 612 can adjust in-band power level of thereceived signal. The adjusted signal can then be fed to a quadraturedemodulator consisting of power splitter 613, I and Q mixers 614, and a90° phase shifter 612. The receive chain 640 can also have a LO 616. Insome embodiments, both the transmit LO 606 and receive LO 616 can becoupled to the same time reference 642. In some embodiments, a single LO616 can synchronize all of the mixers 612, 614 and 604. The timereference 642 can be, for example, a crystal controlled oscillator as ina mobile device. After passing through mixers 614 the signal is thenbaseband. The in-phase component of the signal and the quadrature phasecomponent of the signal can be digitized using a respectiveanalog-to-digital converter (ADC) 615. Digitized sample data streams canthen be output at a port 617 for the I stream and a port 618 for the Qstream.

In some embodiments, the controller 202 can have a transmit processor622 and a receive processor 624 (e.g., the CPU 204). The transmitprocessor 622 and receive processor 624 can be baseband processorshaving separate digital signal processors (DSP) or DSP components. TheseDSPs can perform operations on high data rate at ports 607, 608, 617,618. In some examples this CPU 620 can have an application processorgoverning the operations of the transmit processor 622 and receiveprocessor 624.

In embodiments having only RF transmit chain(s) 630, the CPU 620 mayonly have the transmit processor 622.

The transmit processor 622 can generate a pseudo random number sequenceof +1 and −1 values. These are generated by a Linear Feedback ShiftRegister (LFSR) using a maximal length polynomial known to the server120 for each PON (e.g. the PON 110), for example. Each PON (e.g., thePON 200) can implement a different Polynomial to distinguish its signalat the receiver. In an embodiment, all the PONs 200 in the system 100can use the same polynomial. In the embodiment that uses the samepolynomial, each PON 200 can use a different PN code offset todistinguish its signal at the receiver as is done in CDMA communicationssystems. The sequence may be lowpass filtered in the baseband processor(e.g., the transmit processor 622) to reduce the required RF bandwidth.In other embodiments, the sequence may be left unfiltered, and is thenfed to the transmit chain(s) 630. In an implementation, BPSK modulationcan be used so only one sequence, I, is generated. This sequence is thenfed to a rotator (FIG. 10) that can shift the center frequency by adetermined amount. Despite being fed with a single sequence, the rotatorproduces an I and a Q sequence of samples at ports 607 and 608. Theresult is that the RF signal at the port 601 is a BPSK modulated carrierat frequency that is equal to the sum of the LO frequency and any shiftfrequency added by the rotator. The signal can be BPSK modulated by thepseudo random sequence.

FIG. 10 is a functional block diagram of an embodiment of a portion thepositioning node of FIG. 1. As shown, in FIG. 10, the port 617 and theport 618 can be coupled to Rx I and Rx Q inputs of a rotator 650. Thecontroller 202 can provide a receive (Rx) rotation value. The rotationin the rotator 650 is intended to cancel the rotation superimposed onthe signal by the transmit processor 622. The rotated samples can be fedto a bank of correlators 421 supplied by the same pseudo random sequenceused by the transmit processor 622 above as was used to spread thesignal. The sequence is provided to the mobile device 102 from theserver 120 or identified in the beacon or signal 112 that identifies therespective PON 110.

Each correlator in the bank of correlators 421 can generate a sum of Iand Q values. For example the sum generated for I would correspond tothe sum over a large number of input samples with each input samplemultiplied by one chip of the PN sequence corresponding to a givenhypothesis. These sums can be passed on to the controller 202 through adirect memory access (DMA) interface 422. For each correlatorhypothesis, involving a guess of correct PN code phase and rotationrate, an I_(sum) and a Q_(sum) is generated. The magnitude of the sum isequal to √{square root over (I_(sum) ²+Q_(sum) ²)}. We compute thismagnitude and look for peaks. We will notice a cluster of peaks witheach peak corresponding to a signal from one of the beacons radiatingantennas. The peaks show up spaced in time by the delays introduced bythe saw filters. The phase of each signal is computed by taking thetan⁻¹ (Q_(sum)/I_(sum)) for each correlation peak, using the signs ofI_(sum) and Q_(sum) to resolve the quadrant of the angle. We then adjustthe detected phase by the change of phase that was introduced by thedelays. Then, the phase of the main signal (e.g., the signal 112 a) issubtracted from the phases of each of the delayed copies of the signal112. The result are the carrier phase differences P_(a), P_(b), andP_(c) used in the location calculation for the mobile device 102 and thelocation of the mobile can be determined as outlined by the math abovein connection with FIG. 4 and FIG. 5. FIG. 10 indicates that there isone rotator 650 for each correlation bank 421. An embodiment may havemultiple rotators 650 coupled to subsections of the correlator bank 421in order to search in time and frequency (rotation) simultaneously.

When computing the residual phase, we can be off by one or morewavelengths due to the fact the phase wraps around every 360 degrees.Hence when computing the location solution, we compute the solutionsusing multiple hypotheses for each P_(a), P_(b), and P_(c). Instead ofone computed solution, we end up with multiple possible solutions.Fortunately, it is easy to choose the correct solution using commonsense physical constraints, such as rejecting negative ranges.Additional antennas 610 in the PONs 200 (e.g., the PONs 110) within aroom further add to the robustness of the chosen solution. Other Kalmanfiltering and sensors fusion techniques may be employed to resolve theambiguity.

In the embodiment described above, pseudo random sequences of +1 and −1can be used to modulate the location signal, e.g., the signals 112. Inreality any signal and any modulation can be used. In the receiverwithin the mobile device 102, instead of correlating the received signalagainst a replica of the +1 and −1 pseudo random sequence that was usedto modulate the signal 112, we can instead correlate the received signalagainst delayed copies of itself. This method can produce peaks for eachdelayed copy of the main signal regardless of the type and shape of themain signal. It is important to mention here however that the bandwidthof the main signal dictates the minimum delay that would be needed amongthe delayed copies to tell them apart. More specifically, the larger thebandwidth of the main signal, the smaller the required delays andcorrelation time, need to be. One example could be a variable frequencymodulation, such as a chirp signal. Another example can be to modulatethe carrier with pure noise generated in the beacon (e.g., the PON 110)using natural phenomenon such as diode avalanche noise source. Eventhough the noise signal is totally random and cannot be replicated atthe receiver within the mobile device 102, it can still correlate with adelayed copy of itself at the receiver. Finally, the signal could be thesame signal currently radiated by a standard low energy Bluetooth beaconcurrently used for proximity applications.

In some embodiments, (e.g., those described in connection with FIG. 7)described above, we used SAW delay lines. However, any other delaycomponents and mechanism can be used. When the bandwidth of the radiatedsignal (e.g., the signal 112) is large, the required delay may be small.In this scenario, the delay lines (e.g., the delay lines 704) usingloaded wire traces on printed circuit boards with high permittivity,high dielectric constant, and high permeability, high magnetic constant,could also be used. Meta material structures that result in slow RFgroup delays can also be used.

There are two components that directly affect the accuracy of thelocation determination. The first is the inaccuracy of the LOfrequencies at the beacon and the mobile device. The second is thetemperature drift of the delays of the delay element at the beacon.

The mobile device 102 may be in constant contact with various celltowers in a given cellular system. The mobile device 102 cancontinuously calibrate its LO based on reference signals from thecellular systems. Therefore, the LO in the mobile device 102 may belocked to a very stable frequency reference. Once locked to a cellularfrequency reference, the LO of the mobile device 102 can beat againstthe incoming signal 112 from the PON 110 and can calculate any frequencyerror present the LO 606 in the transmit chain 630 of the PON 200, forexample. Using this procedure, the effect of frequency errors in the LOof the PON 200 and the mobile device 102 can be minimized or eveneliminated.

This is possible because for the most part for indoor positioning themobile device 102 is not moving fast enough relative to the PON(s) 200(e.g., the PON 110) or to a WAN cell to result in significant Dopplershifts between the PON(s) 110 and the mobile device 102 receiving thesignal 112, and between the cellular system reference and the mobiledevice 102. If the mobile device 102 is not connected to a cellularsystem, then any one of a number of frequency references in the air canbe used. In one example, a strong FM station with known frequency can beused. Another is the frequency and time standard broadcast throughoutthe US on 5 MHz, 10 MHz and 20 MHz.

A number of methods can be used to calibrate out the variation in delaysof the delay elements 704 of the PONs 110.

In a first method, the PON 110 can continuously measure the delay andreport it to the mobile device 102. The PON 110 can have a receivingcircuit (e.g., the receive chain 640 of FIG. 9) that compares the timeof arrival between a signal at the transmit port and a delayed copy ofthe signal from one of the outputs of the delay element. Because all thedelay paths use the same delay element substrate, the delays may alllinearly track each other. The delay drift measured on one port givesenough information to predict the drift on all of the other ports. Thisdrift is then reported to the mobile device 102 so that the delay driftscan be accounted for at the receiver of the mobile device 102. Themobile device 102 can also report this information to the server 120 foruse by other mobile devices 102 in the future.

A second solution is for the PON 110 to shift the carrier frequency in apre-determined manner during transmission. This may provide sufficientinformation at the receiver of the mobile device 102 to isolate andaccount for the various element delays.

A third method can implement multiple delayed copies on the same antenna610. In the implementation described in connection with FIG. 8, a singleantenna 610 can transmit one copy of the main signal 112 a delayed bythe delay element. In this implementation the same antenna can alsotransmit another delayed copy distinguishable from the rest by a longerdelay path within the same delay element. The delay network 800 canproduce two distinguishable copies for one of the antennas 610. At thereceiver of the mobile device 102 we are able to measure the differencein delay directly because the signals 122 are transmitted from sameantenna 610. Measuring the time of arrival difference and knowing whatthe delay difference is supposed to be, the delay drift in the delaynetwork 800 can be readily calculated and used to compensate the delaysof all of the other copies of the other antennas 610, if present.

To prolong battery life, the PON 200 may not transmit a location signalcontinuously. The PONs 200 may periodically broadcast an identifyingmessage via, for example, a Bluetooth beacon. The mobile device 102receiving such an identifying message can query the server 120 as to thelocation and characteristics of the PON 200. The mobile device 102 cantransmit a request to the PON 200 to transmit the DSSS location signal(e.g., the signals 112) at a certain power level, duration, andbandwidth. This transmission maybe under control of the server 120. Themobile device 102 can specify the power level, duration, and othercharacteristics of the location signal 112 based on the degree ofaccuracy required by, for example, the mobile device 102. With possiblemultiple requests from multiple mobile devices 102, the PON 200 cantransmit the best possible signal that can be used by all requestingdevices. The PON 200 can transmit the required signal for the durationrequested and the requesting mobile device 102 can determine its ownlocation accordingly. In commercial installations where a source ofpower is available, the PON 200 conservation of battery power may not bea concern. Therefore the PON 200 may instead continuously orperiodically transmit the identifying message as well as the locationDSSS signal without awaiting any request.

In an implementation where the mobile device is the transmitter, themobile contains a transmit chain 630 (FIG. 9) and accompanying supporthardware and software in the baseband and application processors (e.g.,the transmit processor 622 and the receive processor 624). For example,assume the mobile device 102 transmits a DSSS modulated RF signal usinga known pseudorandom number sequence. The same signal 112 can bereceived at each of the individual PON antennas 610 with differentphases depending on the physical relationship between the PON 200 andthe mobile device 102. At the PON 200, two methods can be used tomeasure the phase relationships. One implementation can use a separatereceive chain 640 of FIG. 9 for each antenna 610. In the receiveprocessor 624 each data stream from each receive chain 640 can beprocessed separately and the phase information recovered. The phases canthen be differenced and the required carrier phase differences P_(a),P_(b), and P_(c) can be detected to be used in the position calculationmentioned previously.

An alternate architecture uses an RF switching matrix similar to theswitching matrix 702 (FIG. 7) but used in reverse direction. Now thecommon port of this switching matrix 702 can be coupled to a singlereceive chain 640 (FIG. 9). The other ports of the switching matrix 702can each be connected to separate antennas 610. During reception, theswitching matrix 702 can switch sequentially between each antenna 610and dwell in that connection for a short time. During this time, thedetected phase at the baseband processor (e.g., the receive processor624) can be assigned to the antenna 610 currently connected andreceiving. When the switching matrix 702 switches to another antenna610, the detected phase is assigned to that antenna 610 and so on. Withthis architecture, we can detect the phase of the carrier as received ateach antenna but by using one receive chain 640. So instead of detectingthe carrier phase differences P_(a), P_(b), and P_(c) simultaneously,this architecture detects the phases sequentially. The dwell time islong enough to gather enough signal to result in accurate phaseestimations but not too long that the phase differences change from oneswitching period to another. For typical applications 1-10 milliseconddwell time per antenna 610 should be sufficient for signal to noiseratio (SNR) and short enough for the phases not to have changed due tomobile movement. In the above descriptions, P_(a), P_(b), and P_(c) mayrepresent differences in carrier phases. The same may be true inimplementations using DSSS code phases. With sufficient SNR,interpolation within code phases can also yield a usable estimate of thelength differences among the path from each antenna leading to positionresolution.

Node Synchronization

In order to provide accurate three-dimensional position informationusing OW-TDOA, either the internal clocks of all of the PONs 110 aresynchronized or the time offset is accurately quantified. In embodimentsin which the clocks of the PONs 110 are synchronized, and the mobiledevice 102 can perform calculations based on a single or universaltiming for all of the signals 112 received from the PONs 110.Alternatively, if the clocks of the PONs 110 are not synchronized buttheir time offsets relative to each other are known at the mobile device102, the mobile device 102 can use this measured time offsets to correctfor the lack of synchronization between the PONs 110 and still computeits three-dimensional position.

A two-step process can be implemented to synchronize the PONs 110. Thefirst step is frequency synchronization, followed by timesynchronization, described below. In a first step, the internaloscillators of the PONs 110 lock to a common frequency source. Forexample, this can include synchronizing one or more referenceoscillators (e.g., within the controller 202). Once the clocks of thePONs 110 are synchronized, these clocks may still have arbitrary timeoffsets relative to one another. However, these offsets may remainconstant because all the reference oscillators of the PONs 110 arelocked to a common reference. In some embodiments, it may not becritical that the locked frequency of the PONs 110 have absoluteaccuracy. The important aspect of this synchronization is that the PONs110 has frequency and phase lock with the reference. Phase locking thePONs 110 facilitates carrier phase ranging measurement techniquesresulting in high position accuracy. In addition, smart phones may haveaccurate frequency reference from a cellular network that can calibrateany large frequency offset error between its own internal oscillatorclock and a constellation of PONs 110 within the indoor environment 106.

Frequency Synchronization

In some embodiments several methods may be used to lock the frequency ofthe PONs 110. Some methods can use references that are external to thePONs 110 while other methods can use shared references within the PONs110. For example, an external timing reference can include carrierfrequency of a nearby radio or television broadcast station. The PONs110 can further have a receiver that can tune to the carrier of thelocal TV, radio station, cellular signal, or other radiofrequencysource. The station can provide frequency reference to all the PONs 110tuned to the same station frequency modulated (FM) radio stationsoperating frequencies that are low enough to penetrate to the indoorenvironment 106. For example, one station of note is the WWVB NIST(which is the radio station callsign for the National Institute ofStandards and Technology longwave (60 Kilohertz) Standard Time Signalstation in the United States) and similar stations worldwide such as theNPL NSF signal in the United Kingdom. WWVB is broadcast on 60 kHz and isintended for reception throughout the United States. The PONs 110 canthen use such a radio signal as the reference frequency, thus providingfrequency lock with the other PONs 110 in the indoor environment 106.

However, radio frequencies may not always penetrate to the location ofall of the PONs 110. For example, signal transmitted in the middle ofthe country may be weak on the coasts. In addition, certain radiofrequencies may not have sufficient reception deep indoors, such as witha parking garage.

In an embodiment, one or more of the PONs 110 may be coupled to a mainpower line providing 50 or 60 cycle power. For example, the PON 110 amay be a single antenna PON within a light bulb or smoke detector. ThePON 110 a can thus be coupled to the 50-60 Hz power line frequency tolock the local oscillators of the PON 110 a to a single reference. Theother PONs 110 within CDs can perform a similar synchronization with themain power line. In some examples nominal frequency of given powerlinecan drift by as much as 5%. Thus the absolute value of the frequency maynot be accurate to use as a reference for absolute RF carrier centerfrequency or range measurement. The frequency drifts slowly and over awide geographic area, thus it can still provide a common or relativereference that varies equally across the PONs 110. The mild variationsin frequency or timing can be corrected for as described below.

In some examples, a 50 or 60 cycle powerline signal can be filtered toremove powerline noise and then can be used as a reference to a phaselocked loop (PLL) with a long time constant. Such a time constant may beas long as several seconds or minutes. This 50 or 60 Hz reference drivesits own PLL to generate a frequency that is the same as the nominalfrequency of the reference oscillator 642 in the PON 110. This locallygenerated frequency by the 50 or 60 Hz driven PLL is compared to thereference oscillator 642 within the PON 110. This oscillator 642 can bea crystal oscillator or a ceramic resonator with good absolute accuracybut poor drift performance. Each PON 110 can measure the power linederived frequency against its own local oscillator. Information relatedto the differences between powerline frequency and its own oscillatorcan be provided to the server 120 either through direct coupling of thePONs to the Internet or through a passing by within range mobile device102 with Internet connectivity. The server 120 can store suchinformation and in turn provide timing information to the PONs 110. ThePONs 110 can then use the same divider relationship of the divider inthe PLL that uses the power line as a reference. As a result, all thereference local oscillators 642 within the PONs 110 are slaved to thepower line frequency and hence all the nodes are frequency locked.

A second method can implement a ranging signal emitted by each PON 110to synchronize their respective clocks. Each PON 110 can transmit aranging signal at the same carrier frequencies, for example, BPSK spreadwith various PN spreading codes. If one PON 110 demodulates the rangingsignal from another PON 110, the detected Doppler shift of the receivedsignal can provide a measurement of the reference frequency offset amongthe PONs 110. If each PON 110 adjusts its own local reference oscillatorto drive the median of the Doppler shifts from all the detected signalsto zero, eventually all of the PONs 110 will be frequency-locked to oneanother.

This second method can further improve synchronization by adjusting thedividers of the PLL tracking the 60 Hz of the main powerline to generatea reference frequency identical to the locked frequency obtained fromreceiving the ranging signals of other PONs 110. If the PON 110 isunable to receive the ranging signals from other PONs 110 to maintainfrequency lock for some time, the PONs 110 use this 60 Hz main powerline derived reference to maintain frequency synchronization until itcan receive the ranging signals from the other PONs 110 again.

In another embodiment, each PON 110 can alternately transmit a low powercarrier (e.g., a timing signal) onto the main power for reception by theother PONs 110. If all the PONs 110 can adjust their local referenceoscillator to the median of the injected carriers they receive from theother PONs 110, then eventually frequency synchronization can beachieved. The frequency of the injected carrier can be several orders ofmagnitude above 60 Hz so that the main high voltage frequency can befiltered out at the receiver.

In another embodiment, smoke detectors (e.g., CDs) installed in newconstruction during the last couple of decades all have a low voltagecommon wire tying all the smoke detectors within the same locale (e.g.,the indoor environment 106). This low voltage wire can be used to ensurethat all of the smoke detectors in the same vicinity sound an alarmwhenever any of them detects smoke. The standard indicates that thiswire is kept at low to zero voltage during non-alarm conditions. Anydetector that detects smoke sounds the alarm and raises the voltage onthis wire to 5V-9V. This higher DC voltage is detected by all the othersmoke detector units and all sound the alarm as well. In an embodiment,one of the smoke detectors having a co-located PON 110 can transmit alow voltage AC signal on this wire. Other smoke detectors (e.g., PONs110) can detect this low level AC signal and use it to lock theirreference oscillators thus providing frequency locking among the PONs inthe detectors. Furthermore, this AC signal can be modulated using any ofthe RF modulation techniques known in the field to convey timeinformation as well. This common low voltage signaling using a wire thatis already installed provides a robust way for frequency and timesynchronization among the smoke detectors. The same principle can beimplemented in other systems having for example, wired alarm sensors.

Time Synchronization

The second step in synchronizing the nodes is to measure the time offsetamong the local clocks of the PONs 110 and compensate for them. Threemethods are disclosed herein.

A first method uses two-way WiFi packet exchanges among the PONs 110collocated with light bulbs (e.g., light bulb nodes). The PONs 110 canbe co-located with WiFi modems within the CDs. These WiFi modems may bestandard WiFi modems having an additional capability of precise timingresolution of when a given WiFi packet is transmitted or when another isreceived according to its own local clock. Periodically, with very lowduty cycle that has negligible impact on the WiFi network, each PON 110can engage in a two-way communication with each of the other PONs 110.Because these WiFi modems have a precise timing resolution of the Tx andRx timings of the packets according to their own clocks, after thetwo-way exchanges among all the nodes there would be enough informationto measure and correct all the clock offsets among all the PONs. At thispoint, the PONs 110 may be locked in frequency and aligned in timeenabling the very advantageous OW-TDOA ranging methodology withunlimited simultaneous users (e.g., multiple mobile devices 102), thesame way that is done in GPS. Standard WiFi transceiver were notdirectly designed for ranging purposes. Even though the 802.11 standardstates the turnaround times between receiving a packet and returning anacknowledgment, the allowed tolerance could be as high as 1 microsecond(us) resulting in an error of 300 meters. The embedded WiFi transceiverswithin these CDs and smart bulbs have very precise and calibratedtransmit and receive time stamping and measurement done in hardware inthe physical layer to achieve sub nanosecond timing.

A second method to achieve time synchronization is for each node toalternately inject a narrow pulse into the main power line (e.g., viathe power supply 208) at the zero-crossing moment of the power signal.The transmitter (e.g., the transmitting PON 110) of the pulse would notethe time of transmission according to its own local clock. Other PONs110 can detect this narrow pulse and record the time of detectionaccording to their own local clocks. After each PON 110 has injected ortransmitted its own pulse, all of the transmit and receive timing datais conveyed to the server 120. The server 120 now has sufficient data todetermine all the offsets among the clocks of all of the PONs 110. Thistechnique works because of the assumption that the travel time for anarrow pulse on the power line is equal in both directions between anygiven two PONs 110. It is important to note here that the power line maybe an unmatched, unterminated, and branched network. Hence, we wouldexpect to receive several reflected pulses at the receivers (e.g., thePONs 110) for every injected pulse by a transmitter. The receivers(e.g., the PONs 110) therefore need to be able to isolate these multiplereflected pulses and lock onto the first arriving pulse. This method canuse the low voltage signaling wire that connects all late model smokedetector as mentioned above.

A third method uses the timing of the ranging signal that is emitted byeach PON 110. These ranging signals are described below. In someexamples, the ranging signals can be transmitted at a known and precisetime according to the clock of the transmitting PON 110. Furthermore,these ranging signals can have a structure that allows the receivingPONs 110 to accurately measure the receive time according to the localclock of the receiving PON 110. A protocol after which every PON 110would have received and timed a ranging signal from every other PON 110can generate enough data to compute all the clock offsets among thenodes (e.g., the PONs 110). This process is enabled when the RF pathfrom one node to another is symmetrical in both directions. Thisassumption holds true if the time elapsed in between reversing thedirection of the path is small enough not to encompass indoorenvironmental changes. We will mention more detail of how this is donewhen we describe the emitted ranging signals from the PONs.

We locked the frequencies first because that means that once the clocksof the PONs 110 are aligned they remain aligned. Therefore, we do notneed to repeat the clock synchronization procedure more than once. Inother words, once the nodes (e.g., the PONs 110) are frequency-lockedand clock-aligned, the PONs 110 turn to continuously transmitting theirranging signal and are invisible to any adjacent WiFi network or otherresources that were used to align the clocks.

We see that some of the above frequency locking and time offsetmeasurement and correction procedures require supervision by a dedicatedpositioning server reachable through the internet (e.g., the server120), while others are cooperative among the PONs 1120 and do not needserver intervention.

An alternative to locking the time and frequency of the nodes (e.g., thePONs 110 is to let the node free run. Instead of locking frequency andtime, we measure the differences among the PONs 110 and communicate thefrequency and time offset to the server 120. The mobile device 102entering the indoor environment 106 can receive this information fromthe server 120 and uses it in the equations for determining time thetime of flight of the signals 112 thus nulling the effect of lack ofsynchronization. Measurement of time and frequency offset can be doneexternally to the PONs 110 or internally using one of the methodsoutlined herein. Externally, the mobile device 102 can measure thefrequency offset error among the various PONs 110. This is because thesefrequency offsets show up as carrier Doppler that the mobile device 102can measure and for which it can correct. Timing offsets can be measuredusing a stationary device located somewhere in the vicinity with a knownrelative physical location to the PONs 110. Measured time and frequencyoffsets can then be uploaded to the server to be used by mobile devices.

Positioning Nodes Ranging Signals

The PONs 110, now synchronized, can continuously transmit a multiple ofsignals designed specifically for ranging. To prevent jamming otherwireless equipment operating in the same band, the PONs 110 output poweris set at or below the maximum allowable power mask set by the FCC inthe US and below the more stringent limitation set by the ECC for Europefor unlicensed emitters operating in licensed or unlicensed bands.Complying with both the Federal Communications Commission (FCC) and theElectronic Communications Committee (ECC) power limits insures compliantoperation globally. The masks mentioned are set to regulate theoperation of Ultra-Wideband (UWB) devices and are set at −70 dBm/MHz foroperation from 2.4 GHz to 10 GHz by the ECC. The FCC sets the limit at−41 dBm/MHz. In some embodiments, the PONs 110 can transmit the signals112 at a level below the mask or masks established for (indoor) UWBtransmissions. Accordingly, in some embodiment, the signals 112 can betransmitted at a level below −41 dBm/MHz according to the FCC mask orbelow −70 dBm/MHz according to the ECC mask.

In some embodiments, the PONs 110 can transmit three ranging signals.All are binary phase shift keying (BPSK) modulated and directly spreadusing a pseudo noise (PN) sequence generated by a gold code or a maximallength polynomial linear feedback shift register (LFSR) with a very longperiod, possibly days. The three ranging signals differ from each otherby the degree of position accuracy they enable and by the complexity ofthe receiver that would be required to decode them.

The first signal, we designate LPX, consists of two components LPX1 andLPX2. Each having a center frequency placed within the 2.45 GHz ISM bandand spread with a chipping rate of around 10 Mega Chips Per Second (10MCPS). Typically, LPX1 and LPX2 are positioned as far away as possiblefrom each other within the 2.45 GHz ISM band, to improve wide laneaccuracy, while avoiding strong high duty cycle jammers. LPX1, LPX2center frequencies is chosen by the server as part of radio linkmanagement. LPX2 is also sometime swept from a starting frequency to anending frequency to aid in improved timing recovery.

The second signal, we designate LPY, consists of two components LPY1 andLPY2. LPY1 and LPY2 use a spreading rate of 50 Mega Chips Per Second (50MCPS). LPY1 has a center frequency placed within the 5.8 GHz ISM bandand a null to null bandwidth of 100 MHz. LPY2 is positioned 250 MHz awayon either side of LPY1. This puts LPY2 outside of the 5.8 GHz ISM band.We place LPY1 within the 5.8 GHz band to allow receivers that alreadyhave a 5.8 GHz WiFi receivers to leverage most of their existing RFfront end. At 50 MCPS, receiving and decoding only LPY1 would stillyield useful accuracy. However, for higher accuracy, the receiver canalso receive LPY2. With wide lane techniques applied to 250 MHzseparation, the wide lane wavelength is 1.2 meters making it easy toresolve the integer ambiguity in real time. At 50 MCPS, multipathtransmissions greater than 6 meters can be resolved. So multipatheffects are reduced compared to LPX1 and LPX2 for large venues but arenot eliminated and still limit accuracy in small rooms.

The third signal, we designate LPZ, consists of one component LPZ1placed somewhere within the 3.4 GHz to 10.6 GHz band away from existingjammers and having a spreading rate of 1 Giga 500 Mega Chips Per Second(1 GCPS500 MCPS) which provides greatest accuracy due to robustmultipath resolution capability. At this chipping rate, RF signal pathsdiffering by more than 30 cm are resolved and multipath is greatlymitigated.

The exact center frequencies of these signal components are under thesupervision of the internet-reachable positioning server, such as theserver 120.

For all LPX's, LPY's and LPZ ranging signals, the center frequency ofeach is the same for all the nodes within the vicinity. For example,LPX1 would be transmitted at the same center frequency by all the PONsin the vicinity. The signals are distinguishable from each other usingdifferent code offsets of the PN sequence that is used to spread eachsignal. We can also use entirely different codes to distinguish thesignals as well. CDMA cellular deployments use code offset todistinguish signals from each cell, while GPS uses differing gold codesto distinguish between satellites. Since we are indoors, the distancesare much shorter and the PN code search space is also smaller dues toshorter distances and absence of fast relative movements and hence lowerDoppler search space. Therefore, for our purposes we can use either codeoffset or varying codes to distinguish among the PONs. Our preferredembodiment uses code offsets.

We include these three components of LPX, LPY and LPZ so that mobiledevices (e.g., the mobile device 102) can migrate to higher positionaccuracy in the future as their hardware advances and allows them todecode the higher bandwidth signals that are more demanding to receiveand process. Also, some positioning applications do not need the higheraccuracies and hence the mobile can revert to decoding the lowerbandwidth signal(s) to save cost, complexity and power.

It is important to note that an implementation of the system describedherein may use slightly different center frequencies, power levels,bandwidth, modulation, or spreading rates or codes. In some examples,the nodes (e.g., the PONs 110) broadcast several signals with higher andhigher bandwidth for higher accuracy by more and more complex receivers.The mobile device 102 can also determine its position by receiving anddecoding the PONs transmitted ranging signals using One Way TimeDifference of Arrival (OW-TDOA) from PONs to mobile transmissions thusallowing unlimited simultaneous users. In addition, co-locating the PONs110 in smart light bulbs or other appliances around the house with IOTconnectivity such as connected kitchen appliances for example, allowsfor a continuous source of power and synchronization and eliminates theneed for custom installation and maintenance of the indoor positioningsystem 100. This is especially true if we recognize that most of thelight bulbs are expected to be replaced by smart light bulbs in thecoming years due to more stringent energy saving regulation. Embeddingindoor position location capability within these light bulbs gives theend users further incentive in addition to energy saving to replace thelight bulbs with more efficient ones. PONs could also be located withinpower outlets.

More Details about Using Ranging Signals for Node Synchronization

The following is a description of frequency and time synchronizationmethod using the ranging signals emitted from each node (PON 110) inmore detail.

For all nodes or the PONs 110, LPX1 is continuously transmitted centeredon the same channel. Please note that a node actively transmitting anLPX1 signal cannot receive LPX1's from other nodes because the muchhigher signal level of its own transmitter masks out the much weakersignals from other nodes (PONs 110). So, in order to receive the LPX1signals of other nodes, the local node needs to momentarily turn off itsown transmitter. Doing so allows it to detect the LPX1's from all nearbynodes or PONs 110. If we turn the transmitter on average for half thetime relative to continuous transmission, we lose 3 dB of signal poweras seen by receivers wishing to correlate the LPX1 of this node. Toachieve frequency lock and time synchronization, it is desired for allPONs 110 to detect the LPX1's of all of the nearby PONs 110. Forrobustness, no single PON 110 assumes a master role in thissynchronization and hence all the PONs 110 can run identical protocols.

In some examples, any given node is active for exactly a period T, whereT is in a 10's of microseconds range. After T seconds, the transmitter(e.g., the transmit chain 630) can be deactivated for an arbitraryperiod between 0 and 2T seconds and then reactivated for T seconds againto repeat the cycle. The random off period can change every cycle. Ifall the nodes (PONs 110) do this using different randomizationsequences, then each node can transmit with an average duty cycle of50%. Furthermore, each node can receive the signal from another node,when its transmitter is off and the transmitter of the other node is on,for an average of 25% duty cycle. Therefore, with this method, anoutside receiver receives a signal that is 3 dB lower than if thetransmitters were left on all the time. And the nodes receive the signalpower from other nodes on average 6 dB lower than in the case ofcontinuous transmission. This loss among the nodes can be acceptablesince they can correlate for a long time and since all of them arestationary. The loss for other mobile receiver is well within the systemlimits. By using limits other than 2T, we can change the resulting dutycycles if the application demands it.

To summarize, each node turns on its transmitter for a period T. Thenturns off its transmitter for an arbitrary time between 0 and 2T. Afterthat it turns on its transmitter for a period T and the cycle repeats.The arbitrary time between 0 and 2T is chosen with a uniform probabilitydistribution when averaged over several cycles. It is important thatregardless of the cycling of the state of the transmitter, that the PNsequencers and generators keep running as if the transmitter remainedon. This is important because it allows the receivers to keepcorrelating as if the transmitters are always on; resulting in atolerable power loss of the detected signal of 6 dB and avoids completeloss of synchronization due to the random turn on and turn off times ofthe transmitters.

On the receiver side of the PONs 110, the receivers can insert zerosinto the correlators whenever their transmitters are on to preventself-jamming. As noted above, the nodes can use long period gold codesto spread each of their LPX, LPY and LPZ's. To shorten the correlationsearch times each node can periodically transmit a WiFi packet to theAccess Point (AP) indicating the current time offset from the codestarting state, all ones. Receivers wanting to detect the node, can usethis information to reduce the set of searched hypotheses. Duringinitialization and prior to frequency locking, each node can have afrequency offset relative to other nodes due to local referenceoscillator frequency offset error. The differences in frequencies amongthe nodes show up as imposed Doppler shifts on the received signals byanother node. Prior to frequency locking, each node has atwo-dimensional search space. One dimension looks for the code phase andthe other for the Doppler. Once it detects the signal from as many ofthe surrounding nodes it sees, it makes note of the Doppler imposed oneach received signal from a given node. The receiving node thencalculates the median of the apparent Doppler shifts and slowly slewsits reference oscillator to drive this median Doppler to zero. Thereceiving node also slews the rotators in the base band accordingly tomaintain lock on all the received signals. When this slewing is done byall the nodes, frequency lock is achieved. A receiving node (e.g., PON110) can determine that it is in frequency lock with other nodes when itdoes not see any Doppler and the phase of the received signal fromanother node remains stationary. It is important that the time constantfor the feedback system for slewing the local oscillator be large toprevent locking to wrong solution. This is because it is possible thatthe ranging signal travels from one light bulb (e.g., and collocated PON110) to the next not using Line-Of-Sight (LOS) path. This is becauselight bulbs can be nestled within metal reflectors and that thestrongest path from one ceiling mounted light bulb to the next wouldbounce off metal objects on the floor. For timing purposes, it does notmatter if the path of the signal from one light bulb to the next takesline of sight path or not. This is because we can safely assume that thechannel would be symmetric in both directions and hence the time offlight, despite not being line of sight, would still cancel out. Theforegoing assumes using LPX signals for timing and frequency locking,however, the LPY or LPZ can also be used for the timing and frequencylocking.

If the light bulb and collocated PON 110 is equipped with a receiver(e.g., the receive chain 640) that can decode LPY or LPZ then thisreceiver is able to lock onto the signal and resolve the integer carrierambiguity. This is because the spreading rate of these signals, LPY at50 MCPS and LPZ at 1 GCPS, is high enough so that normal interpolationwithin one chip given a good SNR is sufficient to resolve the integercarrier ambiguity. Once that is resolved, timing synchronization ispossible to a fraction of a nanosecond or better. With LPZ, the highspreading rate allows for multipath resolution and much tighter timesynchronization as well bur requires a more complex receiver.

If the receiving light bulb (and collocated PON 110) uses LPX signalsexclusively, then that bulb can decode LPX1 and LPX2. Using wide lanetechniques, the center frequency difference between LPX1 and LPX2 couldbe as high as 80 MHz. This results in a wide lane wavelength of 3.75meters given the 80 MHz separation. Interpolating within this wavelengthto the resolution typically possible with good SNR resolves the integercarrier ambiguity and leads to sub-nanosecond time synchronization whileonly using LPX signals and hence a simpler low bandwidth receiver ateach bulb.

An alternate method to resolve the carrier integer ambiguity is tosynchronously change the frequency of LPX2. We slide the centerfrequency of LPX2 from 2.41 GHz to higher frequencies both at thetransmitting node and at the receivers of other nodes. As we increasethe frequency of LPX2, and given that the distances between the nodesare fixed, the carrier phase detected at the receivers will change. Ifwe change the frequency from f1 to f2, the phase will change from Phi1to Phi2. We find that the rate of change of the detected phase as afunction of center frequency change is directly related to the distancebetween the nodes. We use this technique to resolve the integer carrierambiguity among the nodes and therefore achieve timing and clocksynchronization among the nodes that is better than a fraction of ananosecond. We describe this technique in more details below.

We start from the state where all the nodes (e.g., the PONs 11) havealready achieved frequency locking by receiving and decoding LPX1 andgoing through the frequency locking method described above. LPX2 is nowlike LPX1 but changes frequency from that of LPX1 to a higher frequencyand back again to the frequency of LPX1. A receiver that locks to LPX1has the same code phase of LPX1. Knowing the code phase of LPX1, thereceiver knows the exact code phase of LPX2 and the instantaneousfrequency shift of LPX2. This is because the timing of the frequencyshift is aligned with the code phase. The receiver, locked on to LPX1,and using this information, synchronously changes the local oscillator(LO) used to receive LPX2 to the instantaneous frequency of LPX2. It cando that because the relationship between the instantaneous frequency ofLPX2 and the LPX1 code phase is known a priori to all the nodes. Undersuch conditions, the LO's of the transmitters and receivers used inLPX2, the receivers being those in a PON 110 or in a mobile devicedetecting a PON ranging signal, are locked in frequency and hence thephase change as a function of LPX2 center frequency is related only tothe distance between the nodes. This technique is good enough to resolvethe carrier integer ambiguity among the nodes and hence allow for veryaccurate timing synchronization among the nodes. With carrier integerambiguity resolved, the timing can be resolved to a fraction of awavelength which is less than a nanosecond at 2.4 GHz. We shift thefrequency of the carrier in our system, because for all intents andpurposes, in our system, everything, e.g., the PONs 110 and the mobiledevice(s) 102, is hardly moving.

Additionally, any information that needs to be communicated between themobile device 102 and the server 120 or the PONs 110 can use forexample, WiFi, Bluetooth, or any other wireless communicationstandard/protocol. Hence LPX, LPY and LPZ may be modulated by aseemingly infinite, uninterrupted, and unaffected by data, PN sequencethat is purely used for ranging and does not carry any information.Hence, there is no restriction on correlation length of time allowingfor high processing gains and much improved SNR. Not having any datamodulated on these ranging signals and locking all the nodes frequenciesallows for theoretically unlimited correlation times and processinggains. These correlation times are limited only by the user dynamicsrequiring faster position update rate. For a mobile device 102 that isstationary or semi-stationary, the correlation time is unrestricted orminimally restricted respectively. This is useful for applications wherehigh positional accuracy and high reliability, and hence high SNR, arerequired for a stationary user.

Returning to frequency locking, we can lock the frequencies of adjacentnodes (e.g., the PONs 110) using either main power line frequencies orby decoding LPX1's of adjacent nodes. A more robust method can combinethese two methods. Relying on LPX1 only means relying on localoscillators within the PON 110 collocated in a light bulb. Theseoscillators have good absolute accuracies, on the order of <100 partsper million, but can drift in a short time specifically as a function oflocal temperature. The main power line however has poor absoluteaccuracy but drifts very slowly with time. In this hybrid method, we usethe median of the LPX1 frequencies of the node as the true absolutefrequency reference. We then measure the local mains power line in termsof this frequency. Subsequently we use the mains as a backup frequencysource anytime there is loss of LPX1 signals. Hence LPX1 method providesthe accurate frequency reference and the mains powerline frequencyprovides the hold over reference in case of loss of LPX1 signaldetection thus keeping all the nodes phase locked.

Multiple Positioning Nodes within a Containing Device

In the following discussion, a PON may refer to the PON 110 having onlyone transmit path (e.g., the transmit chain 630) and one antenna (e.g.,the antenna 610 a) that may or may not have a receiver. In someembodiments, containing devices may contain only one PON 110. However,in some other embodiments, multiple PONs 110 may be collocated within aCD. In order for the mobile device 102 to determine its location, itneeds to detect signals from at least four (4) such PONs 110 (e.g., PONshaving a single antenna). In some instances, it is possible to placemore than one PON 110 within a Containing Device. To be useful, theantennas of each PON should be separated from the antennas 610 of othercollocated PONs 110 by a distance that allow for a good resultant mobilepositional accuracy. The antennas 610 that are very close to each otherresult in Dilution Of Precision (DOP) due to poor geometry among PONs110 and the mobile device 102.

For example, some light tubes can be as long as 5 ft. Building in twoPONs 110 at each end of a light tube may yield sufficient geometry. Morethan two PONs 110 on the same tube may not be advantageous because thePONs 110 would then be collinear and may not yield additional ranginginformation. For this reason, given a room (e.g., the indoor environment106), replacing two non-collinear, spatially separated light tubes withlight tubes having two PONs 110 within them each, may fully instrumentthe room for accurate mobile position determination, provided asufficient number of antennas 610 and signals 110. Please note thatwithin the same Containing Device the two PON 110 circuits would run besynchronized and would share most of their circuit components.

We mention here that the antennas 610 of the PONs 110 may be spacedapart. Therefore, it might be possible in the case of smoke detectors,alarm sensors or light tube ballasts that these CDs would containcircuitry for multiple PONs 110 within them and have low profile RFcables, one cable for each included PON 110, emanating from these CDswith each RF cable terminated by a corresponding antenna 610. In thecase of a smoke detector, these RF cables can be laid in a cross patternon the ceiling. The cables and antenna can be placed above the dry wallceiling to improve aesthetics. The same can be done for alarm sensorsand ballasts, for example. If these antennas 610 at the ends of the RFcables can be spaced apart adequately, one would only need one CD pervicinity for good mobile position determination.

Position Determination Sequence

We now describe the operation of a mobile device that uses the PONs todetermine its indoor location. The third component of the system is theserver 120, communicatively coupled to the network 104 (e.g., theInternet).

We assume that the mobile device 102 already contains a WAN modem, aWiFi or Bluetooth modem and can communicate with a remote server throughthe Internet. Entering a given premises (e.g., the indoor environment106), a mobile device can receive WiFi or Bluetooth signals emitted bythe WiFi or Bluetooth modems in the light bulbs (e.g., the PONs 110) oremitted by, for example, a router installed in the room. Thesetransmissions are not specific to location determination but may be partof registration and connection maintenance with the AP in case of WiFisignals for example. Such transmissions uniquely identify the sender.The PONs 110 may also infrequently use the co-located WiFi or Bluetoothmodems to send Pilot Packets (PP) identifying the nodes (e.g., the PONs110) and conveying code phase information of the PN spreading sequences.The mobile device 102 then communicates with the server 120 (LS) andconveys to the server the ID's of the WiFi or Bluetooth signals it isdetecting. This can indicate to the server 120 coarse positioninformation related to the position of the mobile device 102 within theindoor environment 106.

The mobile device 102 can also convey to the server 120 the desiredlevel of accuracy it needs and what capabilities it has in terms ofbeing able to decode LPX, LPY or LPZ signals. Using this information,the server 120 determines the coarse location of the mobile and conveysto the mobile aiding information about the nearby PONs as well as thestatus of these PONs 110. Such information includes the physicallocation of the PONs 110 relative to the room datum, the centerfrequency of LPX's, LPY's and LPZ ranging signals and the code offset ofeach node along with the code phase. We mentioned previously that thecodes used to spread the ranging signals have a very long cycle.Therefore, exhaustive search for code phase is not feasible. To aid incode acquisition, the Pilot Packets (PP) that the PONs 110 transmitperiodically and/or infrequently, contain the code phase in addition tothe unique identification information that was used to get the correctaiding information. Including the code phase in these Pilot Packetsdrastically reduces the code search space to a handful of code phasecorrelator searcher hypotheses. We also include the code phase with theaiding information from the server 120, but given the unpredictableInternet delays, this still results in a large code search space,especially with the faster chip rate codes of LPY and LPZ. The PilotPackets emitted by each PON 110 are emitted at random times and usingvery low duty cycles, seconds. In some examples, the mobile device 102can receive one PP from one PON 110 to derive all the information itneeds to narrow the search for all the others nearby PONs 110. This isbecause the PONs 110 can all be synchronized and the code offset amongthem is provided in the aiding information packet from the server 120.

Alternatively, the PONs 110 can emit a PN spread ranging signal withmuch shorter code that is aligned with LPX, LPY or LPZ. While shortedcodes have less ranging accuracy, they can be used to find the codephases of the longer codes. This is because searching all possiblehypothesis of the short code is feasible. Once the short code timing isdetected, this timing is used to lock onto the other long codes with thesuperior ranging capabilities. Locking to the short code of one PONuniquely identifies that PON. This information is conveyed to the server120 to obtain the needed aiding information for a position fix.

The mobile device 102 can use all of this information to look for theranging signals. Locking onto the ranging signals with the requiredaccuracy, the mobile device 102 can then to use TDOA technique tomeasure the free air delay from each PON 110 to itself and hence thedistance from itself to each detected PON 110. Knowing these distancesand the location of the PONs 110 as provided by the server 120, themobile device 102 can calculate its position within the room (e.g., theindoor environment 106) relative to the positions of the PONs 110 andthe room datum (e.g., coarse position). The mobile device 102 can thentransmit a report of its own location to the server 120 to aid incontinued system improved accuracy and to optimize performance for allthe mobile devices 102 within the vicinity. The report can include thecalculated position of the mobile device 102, a confidence metric as tothe accuracy of the solution derived from received SNR and multi pathdetection, the detected PONs and which of the LPX, LPY and/or LPZsignals were used in the position determination, along with theirrelative detected power and phase, among other details. The report caninclude the raw timing measurements of the ranging signals as receivedby the mobile device 102.

We mentioned before that mobile devices 102 can have very accuratefrequency reference because of frequency locking to the cellularnetwork. These mobile devices 102 also include in their location reportto the server 120 the frequency offset between their own referenceoscillator and the center frequencies of the PONs 110. This can help theserver 120 detect and instruct the PONs 110 within the vicinity tocorrect their reference oscillators. The report is mainly intended tohelp the server 120 manage the PONs 110 including adjusting the outputpower of each PON 110 to minimize the near-far problem or to directequal PONs 110 signal power to a mobile device 102 on one side of theroom in situations where high accuracy is needed and few if any othermobile devices 102 are in the room. If all the mobile devices 102requiring position solutions within a vicinity (e.g., the indoorenvironment 106) detect a PON 110 signal (e.g., the signals 112) at muchhigher power level than other PON signals, the server can instruct this“loud” PON 110 to reduce output power levels of its ranging signals soas not to mask off signals from other PONs 110.

In some embodiments, as the number of mobile devices 102 in the roomincreases and their physical distribution with the room spreads, it maybecome more difficult to accommodate all of them and the server 120 mayattempt a best effort algorithm to minimize the effect of the near-farissue while maintaining the required fairness towards users. Real-timetransmitted power adjustment as instructed by the server 120 cancompensate for the unpredictable RF environment that the smart lightbulbs smoke detectors or alarm modules (e.g., the PONs 110) wouldexperience within a given light fixtures. For example, one light fixturewould recess the light bulb deep within a metal case while otherfixtures would have the light bulb fully exposed. The RF vicinity. TheRF path attenuation experienced by one bulb detector could differsignificantly differ from RF path attenuation experienced by otherbulbs, detectors, or other CDs. The location reports returned by themobile devices 102 may provide a way to compensate for these variationsand allows the server 120 to adjust the output power of each PON 110.This may reduce the difference in received signal strengths at themobile device 102 from the various PONs 110.

Furthermore, the near-far issue may be further mitigated by the factthat any node 110 transmitter operated 50% of the time can allow for farPONs 110 to be heard.

In some embodiments, two types of location determination can beimplemented. The first location determination method can be initiated bythe mobile device 102, as described above.

A second method for location determination can be initiated by theserver 120. The server 120 can send a location request to the mobiledevice 102. The location request can include the required level ofaccuracy. The mobile device 102 can then initiate an aiding informationrequest similar to that described in connection with the locationdetermination initiated by the mobile device 102. The mobile device 102can elect to accommodate the level of accuracy that is required by therequest from the server 120 or choose a different level of accuracybased on its own capabilities and settings. This can be affected by aprivacy setting implemented at the mobile device 102 (e.g., by theuser). In a private mode, the mobile device 102 can anonymously aidinginformation and may or may not send back an anonymous location report tothe server 120. Similarly, the server 120 can allow various levels ofaccuracy by providing limited aiding information depending on thesettings of the owner of the premises. Encryption may be used for themessages exchanged among the mobile device 102 and the server 120 toprotect privacy and security of the information.

Interchangeable Transmit and Receive Roles

So far we've described that the PONs 110 transmit a ranging signal whilethe mobile device 102 receives the ranging signal(s) and determines itslocation. This is advantageous as it allows for unlimited number ofsimultaneous and demanding users with frequent updates. In somecircumstances, specifically with low number of users with low frequencyof positioning updates, it might be advantageous for the mobile device102 to emit a ranging signal similar to LPX, LPY or LPZ and have thePONs 110 receive the signal and report to the server 120 the respectivetime of arrival of the emitted signal to the server where a position ofthe mobile device is computed. The preferred embodiment of the system isfor the PON 110 to transmit the ranging signal and for the mobiledevices 102 to receive them and determine their location. However, thesystem 100 can operate in either mode and can also operate where thePONs 110 are transmitting the ranging signal (e.g., the signals 112) formobile device 102 to determine their location while at the same timelistening for low duty cycle ranging signals coming from low updatetransmitting mobile devices.

System Installation

In some embodiments, some or all the light bulbs, smoke detectors,and/or alarm modules within the indoor environment 106 can be replacedwith smart devices (or CDs) containing the PONs 110. For properoperation, these PONs 110 need to frequency lock and synchronize amongthemselves as described in the foregoing. In addition, the physicallocation of the CDs/PONs 110 should be known to the server 120 so thatthe server 120 can convey this information as part of the aidinginformation packet it sends to the mobile device 102 entering the indoorenvironment 106. It is important to note here that the physical positionof the PON 110 relates to the center of radiation of the antenna 610used by the PON 110. This may or may not correspond to a physicalfeature of the light bulb smoke detector or alarm sensor so physicalsurveying methods, such as surveying equipment, may not yield thedesired values. Instead, we shall use an inverse algorithm to determinethe physical locations as needed by the server for proper and accurateoperation.

From the foregoing, the mobile device 102 should detect the signals(e.g., the signals 112) from, and measure the distance to, a minimum offour PONs to determine the location of a mobile within the room. Theminimum of four PONs 110 is predicated on each PON 110 having a singleantenna 610. If the PONs 110 have more than one antenna 610, the numberrequired may decrease. For ease of description, the following assumesthe PONs 110 have one antenna 610.

In reverse, if the mobile device 102 measures the ranging signals fromall the PONs 110 at four known points within the room, then there issufficient information to determine the location of all the PONs 110, orthe CDs, as the case may be.

For example, assuming that CDs or the smart light bulbs, smokedetectors, and alarm sensors containing PONs 110 are already installed,are communicating with the server 120, and that their PONs 110 havealready achieved frequency lock and clock time alignment. Let's alsoassume that our datum for the room (e.g., the indoor environment 106) isthe point where the right side of the door frame on the entry of theroom intersects the floor. The mobile device 102 having the requiredhardware and software to receive the ranging signals 112 emitted by thePONs 110 can be configured in a survey mode rather than normal,location-determination mode. Survey mode, in this example, performs allthe operation as in normal mode except instead of calculating theposition and returning that to the server 120 it only returns to theserver 120 the TDOA of all the ranging signals 112 received by themobile device 102. In survey mode, the mobile device 102 can be placedsequentially in various locations (e.g., at the 4 corners) of the doorat the entry of the indoor environment 106. The mobile device 102 canthen perform required RF measurements and convey the results to theserver 120 along with an identification of the corner at which themeasurement was taken. From such measurements, the server 120 now hassufficient information to determine the location of the PONs 110 withinthe space (e.g., the indoor environment 106).

An alternate method is to slowly trace the frame of the door with themobile device 102. The mobile device 102 can take continuous readingsalong each side. This method may also give sufficient information toyield the position of the PONs 110. Since the door frame is typicallyplanar, there is an ambiguity about which side of the door the PONs 110reside. One additional measurement at any point inside the room insufficient to resolve this ambiguity. Finally, the dimensions of thedoor need to be measured and conveyed to the server 120. This is easysince in most buildings, the doors are of equal size. The method yieldsas good of an accuracy as how accurately the user places the mobile whenprompted. It is simple and perhaps accurate enough for residentialapplications and office spaces.

Another method yielding higher accuracy uses a rigid board with four ormore receiving antennas used by special receiving hardware thatalternately uses and processes signals from each antenna. The antennaslocations relative to themselves and relative to a clear datum on theboard are precisely set during manufacturing. We place this board withinthe room and the receiver in the board proceeds to take measurementsfrom each antenna in turn and conveys the information wirelessly to theserver 120. Because of the precise relative location of these antennasto themselves and to the datum point on the board, we now know withprecision the location of the PONs 110 relative to the location of theseantennas and the datum on the board. We use survey techniques to relatethe datum point indicated on this board to a datum point of the room,such as a door corner. This relative location between the two datums isuploaded to the server. This technique may be more useful for commercialinstallations.

One can envision other techniques with varying complexity and accuracyto map the locations of the PONs 110 and upload them to the server 120.The main theme here however is placing the mobile device 102 orequivalently equipped receiver at four or more known points within theroom and conveying the measurements of the TDOA among the detected PONs110 to the server 120. From this information, the server 120 candetermine the position of the PONs 110 within a space. The more accuratewe place the surveying receiver during these measurements, the moreaccurate the calculation of the position of the PONs 110 will be.

One feature of the system is detection of positional errors of the PONs110. Some light bulbs could be installed in portable movable fixtures.As noted above, before the mobile device 102 can determine its location,it transmits a location report to the server 120 including the computedlocation of the mobile device 102. Such a report may contain the rawtiming of the ranging signals as seen by the mobile device 102. If anyfixture smoke detector or alarm sensor is moved, it's timing relative toother PONs 110 changes from what was measured during clock alignment.Also, in an over-determined solution, the mobile device 102 can detectthat based on time measurement, no reasonable solution can be returned,given the stated positions of the PONs 110 as recorded at the server120. This gives enough information for the server 120 to detect that oneor more PONs 110 have moved. At this point, the system 100 (e.g., theserver 120) can initiates a synchronization procedure to realign theclocks of each of the PONs 110. In addition, the redundant locationsolutions can be used to determine which fixture has moved and to where.Once the clocks are realigned and the new location of the fixture or CDis determined, the server 120 is ready again to provide consistentaiding information. All the above happens automatically because themobile devices 102 can continuously share the location report data withthe server 120 after a location determination operation.

In an embodiment, the server 120 can instruct the mobile device 102 whento send the location determination report. For example, once a mobiledevice 102 enters the room, and receives the aiding information from theserver 120, it generally does not need to get the aiding informationpacket for subsequent position updates. This is because the aidinginformation does not change frequently within the same vicinity (e.g.,the indoor environment 106). Also, the server 120 may not want toreceive a location determination report from the mobile device 102 afterevery location update. The server 120 therefore can instruct the mobiledevice 102 as to the frequency of when to send a report or alternatelyspecify events after which a report is desired such as a minimumdistance movement. The above reduces the amount of traffic that isexchanged between the mobile devices 102 and the server 120. Forexample, in congested venues, the server 120 may request locationreports from a few of the mobile devices 102 present. It also may limitthe content of the report. For example, the server 120 may instruct oneor more mobile devices 102 to send location reports containing onlytheir locations, allowing other mobile devices 102 in the vicinity tosend more or additional information. This can reduce the requiredtraffic while maintaining all the functionality of continuous tuning andperformance enhancement.

Those of skill will appreciate that the various illustrative logicalblocks (e.g., the various servers described herein), modules, andalgorithm steps described in connection with the embodiments disclosedherein can often be implemented as electronic hardware, computersoftware, or combinations of both. To clearly illustrate thisinterchangeability of hardware and software, various illustrativecomponents, blocks, modules, and steps have been described abovegenerally in terms of their functionality. Whether such functionality isimplemented as hardware or software depends upon the design constraintsimposed on the overall system. Skilled persons can implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the disclosure. In addition, the grouping offunctions within a module, block or step is for ease of description.Specific functions or steps can be moved from one module or blockwithout departing from the disclosure.

The various illustrative logical blocks and modules (e.g., the variousservers described herein) described in connection with the embodimentsdisclosed herein can be implemented or performed with a general purposeprocessor, a digital signal processor (DSP), application specificintegrated circuit (ASIC), a field programmable gate array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor canbe a microprocessor, but in the alternative, the processor can be anyprocessor, controller, microcontroller, or state machine. A processorcan also be implemented as a combination of computing devices, forexample, a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

The steps of a method or algorithm described in connection with theembodiments disclosed herein can be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module can reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium. An exemplary storage mediumcan be coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium can be integral to the processor. Theprocessor and the storage medium can reside in an ASIC.

It will be understood that the benefits and advantages described abovemay relate to one embodiment or may relate to several embodiments. Theembodiments are not limited to those that solve any or all of the statedproblems or those that have any or all of the stated benefits andadvantages.

Any reference to ‘an’ item refers to one or more of those items. Theterm ‘comprising’ is used herein to mean including the method blocks orelements identified, but that such blocks or elements do not comprise anexclusive list and a method or apparatus may contain additional blocksor elements.

What is claimed is:
 1. A system for determining a location of a mobiledevice within an indoor environment, the system comprising: a firstpositioning node (PON) configured to transmit a first modulated signal;a second PON disposed in a different location than the first PON andconfigured to transmit a second modulated signal; and a serverconfigured to receive a request from the mobile device indicating acoarse location of the mobile device, transmit location information forthe first PON and the second PON based on the request, and signalinformation related to the first modulated signal and the secondmodulated signal; and receive a position report from the mobile device,the position report being based on a difference in time between thefirst modulated signal and the second modulated signal at a time ofarrival at the mobile device.
 2. The system of claim 1 wherein thesecond modulated signal is synchronized in time and frequency with thefirst modulated signal at a time of transmission.
 3. The system of claim1 wherein the first PON and the second PON are collocated with acontaining device, the containing device being an in-home electronicdevice.
 4. The system of claim 2 wherein the first modulate signal andthe second modulated signal are transmitted below an ultra-wideband(UWB) mask set for indoor UWB transmissions.
 5. The system of claim 1wherein the first modulated signal and the second modulated signal aredirect sequence spread spectrum (DSSS) signals separated by at least onespreading chip.
 6. The system of claim 1 wherein the first PON and thesecond PON are collocated within a single containing device.
 7. Thesystem of claim 1 wherein the first PON and the second PON are disposedwithin different containing devices.
 8. The system of claim 7 whereinthe first PON and the second PON are coupled to a common power main andare configured to synchronize the first modulated signal and the secondmodulated signal based on a frequency of the common power main.
 9. Thesystem of claim 8 wherein, the first PON is further configured totransmit a first timing signal via the power main; the second PON isfurther configured to transmit a second timing signal via the powermain, the first timing signal and the second timing signal having afrequency several orders of magnitude the frequency of the common powermain; the first PON is further configured to adjust a local referenceoscillator based on the second timing signal and one or more receivedother timing signals; and the second PON is further configured to adjusta local reference oscillator based on the first timing signal and theone or more received other timing signals.
 10. The system of claim 1wherein the first PON and the second PON are configured to: receive oneor more other modulated signals; determine a frequency and time offsetbetween a respective one of the first modulated signal and the secondmodulated signal and the one or more other modulated signals; and adjusta frequency of the respective one of the first modulated signal and thesecond modulated signal to synchronize frequency and time with the oneor more other modulated signals.
 11. The system of claim 1 wherein thefirst modulated signal and the second modulated are transmittedintermittently at the respective first PON and second PON.
 12. A methodfor determining a location of a mobile device within an indoorenvironment, the method comprising: transmitting, by a first positioningnode (PON), a first modulated signal; transmitting, by a second PONdisposed in a different location than the first PON, a second modulatedsignal ; receiving, at a server, a request from the mobile deviceindicating a coarse location of the mobile device; transmitting, by theserver, location information related to first PON and the second PONbased on the request, and signal information related to the firstmodulated signal and the second modulated signal; and receiving, at theserver, a position report from the mobile device, the position reportbeing based on a difference in time between the first modulated signaland the second modulated signal at a time of arrival at the mobiledevice.
 13. The method of claim 12 wherein the second modulated signalis synchronized in time and frequency with the first modulated signal ata time of transmission.
 14. The method of claim 12 wherein the first PONand the second PON are collocated with a containing device, thecontaining device being an in-home electronic device.
 15. The method ofclaim 12 wherein the first modulated signal and the second modulatedsignal are direct sequence spread spectrum (DSSS) signals separated byat least one spreading chip.
 16. The method of claim 12 wherein thefirst PON and the second PON are coupled to a common power main and areconfigured to synchronize the first modulated signal and the secondmodulated signal based on a frequency of the common power main.
 17. Themethod of claim 16 wherein, the first PON is further configured totransmit a first timing signal via the power main; the second PON isfurther configured to transmit a second timing signal via the powermain, the first timing signal and the second timing signal having afrequency several orders of magnitude the frequency of the common powermain; the first PON is further configured to adjust a local referenceoscillator based on the second timing signal and one or more receivedother timing signals; and the second PON is further configured to adjusta local reference oscillator based on the first timing signal and theone or more received other timing signals.
 18. A method for determininga location of a mobile device within an indoor environment having one ormore positioning nodes (PONs), the method comprising: determining, at amobile device, a coarse location of the indoor environment; transmittinga request to a server including the coarse location; receiving aidinginformation from the server based on the coarse location; receiving afirst positioning signal from a first antenna; receiving a secondpositioning signal from a second antenna, the second positioning beingout of phase with the first positioning signal; receiving a thirdpositioning signal from a third antenna, the third positioning signalbeing out of phase with the first positioning signal and the secondpositioning signal; and determining a position of the mobile devicebased on a one-way time-difference of arrival (TDOA) between the firstpositioning signal, the second positioning signal, and the thirdpositioning signal.
 19. The method of claim 18, wherein the firstpositioning signal, the second positioning signal, and the thirdpositioning signal are transmitted using direct sequence spread spectrum(DSSS).
 20. The method of claim 18, wherein the first antenna, thesecond antenna, and the third antenna are collocated within the samePON.